If you have foo and foo.git in GITDIR, the two can end up being confused
by git with some horrible union of the two being cloned. This adds
a workaround to avoid this happening until git 1.7.9.2 onwards is
common enough for this to be removed. We use a symlink to hide
the directories we don't want git to know about.
(Bitbake rev: bbf1f6fe594c721a296ca09ee7c583d4a205c591)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>