diff --git a/poky/scripts/lib/buildstats.py b/poky/scripts/lib/buildstats.py
index d9aadf3..f7db3ea 100644
--- a/poky/scripts/lib/buildstats.py
+++ b/poky/scripts/lib/buildstats.py
@@ -263,7 +263,7 @@
         """Aggregate other buildstats into this"""
         if set(self.keys()) != set(buildstats.keys()):
             raise ValueError("Refusing to aggregate buildstats, set of "
-                             "recipes is different")
+                             "recipes is different: %s" % (set(self.keys()) ^ set(buildstats.keys())))
         for pkg, data in buildstats.items():
             self[pkg].aggregate(data)
 
diff --git a/poky/scripts/lib/checklayer/__init__.py b/poky/scripts/lib/checklayer/__init__.py
index 7788041..670f0ee 100644
--- a/poky/scripts/lib/checklayer/__init__.py
+++ b/poky/scripts/lib/checklayer/__init__.py
@@ -196,38 +196,36 @@
     if layer_depends is None:
         return False
     else:
-        # Don't add a layer that is already present.
-        added = set()
-        output = check_command('Getting existing layers failed.', 'bitbake-layers show-layers').decode('utf-8')
-        for layer, path, pri in re.findall(r'^(\S+) +([^\n]*?) +(\d+)$', output, re.MULTILINE):
-            added.add(path)
+        add_layers(bblayersconf, layer_depends, logger)
 
-        for layer_depend in layer_depends:
-            name = layer_depend['name']
-            path = layer_depend['path']
+    return True
+
+def add_layers(bblayersconf, layers, logger):
+    # Don't add a layer that is already present.
+    added = set()
+    output = check_command('Getting existing layers failed.', 'bitbake-layers show-layers').decode('utf-8')
+    for layer, path, pri in re.findall(r'^(\S+) +([^\n]*?) +(\d+)$', output, re.MULTILINE):
+        added.add(path)
+
+    with open(bblayersconf, 'a+') as f:
+        for layer in layers:
+            logger.info('Adding layer %s' % layer['name'])
+            name = layer['name']
+            path = layer['path']
             if path in added:
-                continue
+                logger.info('%s is already in %s' % (name, bblayersconf))
             else:
                 added.add(path)
-            logger.info('Adding layer dependency %s' % name)
-            with open(bblayersconf, 'a+') as f:
                 f.write("\nBBLAYERS += \"%s\"\n" % path)
     return True
 
-def add_layer(bblayersconf, layer, layers, logger):
-    logger.info('Adding layer %s' % layer['name'])
-    with open(bblayersconf, 'a+') as f:
-        f.write("\nBBLAYERS += \"%s\"\n" % layer['path'])
-
-    return True
-
-def check_command(error_msg, cmd):
+def check_command(error_msg, cmd, cwd=None):
     '''
     Run a command under a shell, capture stdout and stderr in a single stream,
     throw an error when command returns non-zero exit code. Returns the output.
     '''
 
-    p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, cwd=cwd)
     output, _ = p.communicate()
     if p.returncode:
         msg = "%s\nCommand: %s\nOutput:\n%s" % (error_msg, cmd, output.decode('utf-8'))
@@ -257,7 +255,7 @@
         os.unlink(sigs_file)
     try:
         check_command('Generating signatures failed. This might be due to some parse error and/or general layer incompatibilities.',
-                      cmd)
+                      cmd, builddir)
     except RuntimeError as ex:
         if failsafe and os.path.exists(sigs_file):
             # Ignore the error here. Most likely some recipes active
diff --git a/poky/scripts/lib/devtool/standard.py b/poky/scripts/lib/devtool/standard.py
index d14b7a6..b7d4d47 100644
--- a/poky/scripts/lib/devtool/standard.py
+++ b/poky/scripts/lib/devtool/standard.py
@@ -509,6 +509,11 @@
             if not 'flag' in event:
                 if event['op'].startswith(('_append[', '_prepend[')):
                     extra_overrides.append(event['op'].split('[')[1].split(']')[0])
+        # We want to remove duplicate overrides. If a recipe had multiple
+        # SRC_URI_override += values it would cause mulitple instances of
+        # overrides. This doesn't play nicely with things like creating a
+        # branch for every instance of DEVTOOL_EXTRA_OVERRIDES.
+        extra_overrides = list(set(extra_overrides))
         if extra_overrides:
             logger.info('SRC_URI contains some conditional appends/prepends - will create branches to represent these')
 
@@ -769,9 +774,13 @@
             check_commits = True
         else:
             if os.path.exists(os.path.join(srctree, '.git')):
-                # Check if it's a tree previously extracted by us
+                # Check if it's a tree previously extracted by us. This is done
+                # by ensuring that devtool-base and args.branch (devtool) exist.
+                # The check_commits logic will cause an exception if either one
+                # of these doesn't exist
                 try:
                     (stdout, _) = bb.process.run('git branch --contains devtool-base', cwd=srctree)
+                    bb.process.run('git rev-parse %s' % args.branch, cwd=srctree)
                 except bb.process.ExecutionError:
                     stdout = ''
                 if stdout:
diff --git a/poky/scripts/lib/wic/engine.py b/poky/scripts/lib/wic/engine.py
index 4662c66..ea600d2 100644
--- a/poky/scripts/lib/wic/engine.py
+++ b/poky/scripts/lib/wic/engine.py
@@ -245,9 +245,16 @@
         self._ptable_format = None
 
         # find parted
-        self.paths = "/bin:/usr/bin:/usr/sbin:/sbin/"
+        # read paths from $PATH environment variable
+        # if it fails, use hardcoded paths
+        pathlist = "/bin:/usr/bin:/usr/sbin:/sbin/"
+        try:
+            self.paths = os.environ['PATH'] + ":" + pathlist
+        except KeyError:
+            self.paths = pathlist
+
         if native_sysroot:
-            for path in self.paths.split(':'):
+            for path in pathlist.split(':'):
                 self.paths = "%s%s:%s" % (native_sysroot, path, self.paths)
 
         self.parted = find_executable("parted", self.paths)
@@ -331,7 +338,7 @@
     def copy(self, src, pnum, path):
         """Copy partition image into wic image."""
         if self.partitions[pnum].fstype.startswith('ext'):
-            cmd = "echo -e 'cd {}\nwrite {} {}' | {} -w {}".\
+            cmd = "printf 'cd {}\nwrite {} {}' | {} -w {}".\
                       format(path, src, os.path.basename(src),
                              self.debugfs, self._get_part_image(pnum))
         else: # fat