--replace-all so we don't accum variables

Review URL: http://codereview.chromium.org/504002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@34500 0039d316-1c4b-4281-b951-d872f2087c98

git_cl_hooks.py

@@ -58,7 +58,7 @@ def RunHooks(hook_name, upstream_branch):
     watchlist = watchlists.Watchlists(options.change.RepositoryRoot())
     files = [f.LocalPath() for f in options.change.AffectedFiles()]
     watchers = watchlist.GetWatchersForPaths(files)
-    Backquote(['git', 'config', '--add',
+    Backquote(['git', 'config', '--replace-all',
                'rietveld.extracc', ','.join(watchers)])
 
   # Run the presubmit checks.