[PATCH 0 of 7] subrepo compatibility with pre-1.7 git

[Eric Eisner]

This series aim for test passing with git 1.5.6.5, the oldest version anyone has asked me about and apparently the version in debian stable.

All of the changes seem pretty neutral except for silencing git output in the test (which had some useful branch info in it), and the switch to reading the verbose status output. If anyone has a better solution to implementing dirty() let me know.