Fix rebase-update on windows on git-svn repos.

Through a comedy of wrapper scripts, the ^ is being swallowed, which
causes the `git config` invocation to match all lines which HAVE
"remote" in them, instead of matching lines which BEGIN with remote.

R=maruel@chromium.org, pkasting@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1566343002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@298185 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/git_rebase_update.py b/git_rebase_update.py
index a725207..1126c94 100755
--- a/git_rebase_update.py
+++ b/git_rebase_update.py
@@ -49,9 +49,8 @@
   remotes = set()
   tag_set = git.tags()
   fetchspec_map = {}
-  all_fetchspec_configs = git.run(
-      'config', '--get-regexp', r'^remote\..*\.fetch').strip()
-  for fetchspec_config in all_fetchspec_configs.splitlines():
+  all_fetchspec_configs = git.config_regexp(r'^remote\..*\.fetch')
+  for fetchspec_config in all_fetchspec_configs:
     key, _, fetchspec = fetchspec_config.partition(' ')
     dest_spec = fetchspec.partition(':')[2]
     remote_name = key.split('.')[1]