Fixed chromite shell to report python errors

bin/chromite

 #!/usr/bin/python
 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Wrapper for the chromite shell.
 
 This script is intended to run in several ways:
 - Outside the chroot, it should be _copied_ to someplace that is in the
   path (like depot_tools).  It will search for the right chromite by looking
@@ skipping 37 matching lines @@
       yield [path]
       path, prev_path = os.path.dirname(path), path
 
 
 for path in Search(os.getcwd()):
   sys.path = path + sys.path
   try:
     import chromite.shell.main
     break
   except ImportError, e:
+    # Just in case there is actually something wrong with Chromite, print
+    # a sensible error. We match only the end of the string so that we can
+    # handle an error within the chromite directory.
+    # The full error is 'No module named (chromite.)shell.main'
+    # Note: If you hit the directory containing chromite on the way up, then
+    # the error will be 'No module named shell.main' so we must check only the
+    # shell.main part.
+    if not str(e).endswith('shell.main'):
+      raise
+
     # We've got different modules named chromite in the tree, pulling in the
     # wrong one will break the right one.  So unload it.
     if 'chromite' in sys.modules:
       del sys.modules['chromite']
     sys.path = sys.path[len(path):]
 else:
   # TODO(dianders): Should we actually print out the 'repo init' call that
   # the user should use?
   sys.stderr.write(
       "ERROR: Couldn't find the chromite tool.\n"
       "\n"
       "Please change to a directory inside your Chromium OS source tree\n"
       "and retry.  If you need to setup a Chromium OS source tree, see:\n"
       "  http://www.chromium.org/chromium-os/developer-guide\n")
   sys.exit(1)
 
 chromite.shell.main.main()