Git: Recognize SHA1s from 7 to 40 digits.

Qt's grafts have 9-digit SHA1s which did not work
with the previous 7-8/40 character limits.

Change-Id: I3989405d00b575a6efb7dc6a467cbb24df9f3db5
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>