Enforce inserting the depot_tools path as the first path in sys.path.

Otherwise if there is a file named breakpad.py for instance in the current
directory, it will be loaded instead of the one in depot_tools.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6312034

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@73165 0039d316-1c4b-4281-b951-d872f2087c98

git-cl-upload-hook

@@ -28,7 +28,7 @@ if not depot_tools_path:
 # If we found depot_tools, add it to the script's import path.
 # Use realpath to normalize the actual path
 if depot_tools_path:
-  sys.path.append(os.path.realpath(depot_tools_path))
+  sys.path.insert(0, os.path.realpath(depot_tools_path))
 else:
   print "ERROR: Could not find depot_tools in your PATH."
   print "ERROR: Please add it to your PATH and try again."