git-remote-testgit: fix error handling

If fast-export did not complete successfully the error handling code
itself would error out.

This was broken in commit 23b093ee0 (Brandon Casey, Wed Jun 9 2010,
Remove python 2.5'isms). Revert that commit an introduce our own copy
of check_call in util.py instead.

Tested by changing 'if retcode' to 'if not retcode' temporarily.

Signed-off-by: Sverre Rabbelier <srabbelier@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git_remote_helpers/git/exporter.py

@@ -2,6 +2,8 @@ import os
 import subprocess
 import sys
 
+from git_remote_helpers.util import check_call
+
 
 class GitExporter(object):
     """An exporter for testgit repositories.
@@ -53,6 +55,4 @@ class GitExporter(object):
 
         args = ["sed", "s_refs/heads/_" + self.repo.prefix + "_g"]
 
-        child = subprocess.Popen(args, stdin=p1.stdout)
-        if child.wait() != 0:
-            raise CalledProcessError
+        check_call(args, stdin=p1.stdout)