add should respect .gitignore

[RadicalZephyr]

We probably want to add a -f option to override this, but in general we should check whether the git add succeeds on each file we try to add, and move it back out of the hermit profile if the add fails. This way we can respect the user's local and global .gitignore.

[reillysiemens]

This is a very good idea. We should definitely do this.