Fix a bug in gclient recurse for git-svn users. Make gclient_utils.CheckCall more versatile.

gclient.py

Index: gclient.py
diff --git a/gclient.py b/gclient.py
index 9cf30c76cb6fb4bb659f71f153549452bca6433e..989a1c418d5ec309204a778131ed68ebe8ed0dcc 100644
--- a/gclient.py
+++ b/gclient.py
@@ -888,9 +888,12 @@ def CMDrecurse(parser, args):
     if scm_set and scm not in scm_set:
       continue
     cwd = os.path.normpath(os.path.join(root, path))
-    env['GCLIENT_SCM'] = scm
-    env['GCLIENT_URL'] = url
-    subprocess.Popen(args, cwd=cwd, env=env).communicate()
+    if scm:
+      env['GCLIENT_SCM'] = scm
+    if url:
+      env['GCLIENT_URL'] = url
+    gclient_utils.Popen(args, cwd=cwd, env=env).communicate()
+  return 0
 
 
 @attr('usage', '[url] [safesync url]')