Fix retrying on HTTP 502, my last patch remove this specific case.

svn's client uses a different error format for HTTP 502 and I didn't recall how
the string was formatted. Luckily enough googlecode fails often enough it wasn't
long for me to reproduce the issue. :)

TBR=bradnelson

Review URL: http://codereview.chromium.org/3143030

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@56675 0039d316-1c4b-4281-b951-d872f2087c98

scm.py

@@ -451,7 +451,8 @@ class SVN(object):
             if (x.startswith('svn: OPTIONS of') or
                 x.startswith('svn: PROPFIND of') or
                 x.startswith('svn: REPORT of') or
-                x.startswith('svn: Unknown hostname')):
+                x.startswith('svn: Unknown hostname') or
+                x.startswith('svn: Server sent unexpected return value')):
               return True
           return False