Display base correctly for git-svn in update history

Summary:
for a git repo which is using git-svn, we should show the
revisioni number. For example, it is show "svn+ssh" if the git url
starts with "svn+ssh". Show the svn revision number instead.

Before fix:
https://secure.phabricator.com/file/view/PHID-FILE-j5rogyqjkgifoxtpwzcu/

After fix:
https://secure.phabricator.com/file/view/PHID-FILE-4vsnptcjzuzuyj4zo25x/

Test Plan:
- verified a diff with git-svn worked
- verified a pure git diff still worked

Reviewers: epriestley, nh

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1344

src/applications/differential/view/revisionupdatehistory/DifferentialRevisionUpdateHistoryView.php

@@ -1,7 +1,7 @@
 <?php
 
 /*
- * Copyright 2011 Facebook, Inc.
+ * Copyright 2012 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -308,11 +308,19 @@ final class DifferentialRevisionUpdateHistoryView extends AphrontView {
   private function renderBaseRevision(DifferentialDiff $diff) {
     switch ($diff->getSourceControlSystem()) {
       case 'git':
-        return substr($diff->getSourceControlBaseRevision(), 0, 7);
+        $base = $diff->getSourceControlBaseRevision();
+        if (strpos($base, '@') === false) {
+          return substr($base, 0, 7);
+        } else {
+          // The diff is from git-svn
+          $base = explode('@', $base);
+          $base = last($base);
+          return $base;
+        }
       case 'svn':
         $base = $diff->getSourceControlBaseRevision();
         $base = explode('@', $base);
-        $base = end($base);
+        $base = last($base);
         return $base;
       default:
         return null;