[PATCH 0 of 5] gitsubrepo bugfixes and status

[Eric Eisner]

The first 4 patches are bugfixes. The backout shows that I should test with
old git before sending.

The status patch gives the most useful subset of status behavior, only
reporting added, modified, or removed files. This implementation is very
simple and version-portable; I couldn't find a way to give the full
functionality without parsing a series of high-level commands.