jgit-describe only supports 1 subdir atm, so for now we still need to shell out once.
Change-Id: I1cdbfd09abe2f515b78732e98203c52772a724c6
Reviewed-on: http://gerrit.dmdirc.com/2299
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>