use origin as first pull try in test_pr

prevents 'your branch is ahead of origin/master by xx commits' messages from growing over time.

tools/test_pr.py

@@ -87,7 +87,7 b' class TestRun(object):'
         os.chdir(repodir)
         check_call(['git', 'checkout', 'master'])
         try :
-            check_call(['git', 'pull', ipy_repository, 'master'])
+            check_call(['git', 'pull', 'origin', 'master'])
         except CalledProcessError :
             check_call(['git', 'pull', ipy_http_repository, 'master'])
         os.chdir(basedir)