Run commands via git-shell

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Fix typo in comment

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Refactor attach/exit handling

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Don't panic

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Be really strict about incoming command

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>