Fix upload.py with git when diff.external is set.

Review URL: http://codereview.chromium.org/113586

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@16476 0039d316-1c4b-4281-b951-d872f2087c98

upload.py

@@ -1004,7 +1004,8 @@ class GitVCS(VersionControlSystem):
     # the hashes of the base files, so we can upload them along with our diff.
     if self.options.revision:
       extra_args = [self.options.revision] + extra_args
-    gitdiff = RunShell(["git", "diff", "--full-index"] + extra_args)
+    gitdiff = RunShell(["git", "diff", "--no-ext-diff", "--full-index"] +
+                       extra_args)
     svndiff = []
     filecount = 0
     filename = None