mock stdout for dumpdata, part of bug 1141023
mock stdout for dumpdata, part of bug 1141023

dumpdata.handle used to return the string in 1.4.x, and doesn't with
1.5. mock stdout with a StringIO and get the output value from that.

Also, use call_command, which handles arguments much better for us.

Pike/elmo,Pike/elmo,Pike/elmo,mozilla/elmo,mozilla/elmo,mozilla/elmo,Pike/elmo,mozilla/elmo