Use eclass git-2; eclass git received last rites

See: http://thread.gmane.org/gmane.linux.gentoo.devel/86980

The former eclass git has been superseded by the new eclass git-2.
For more information please refer to the discussion on the gentoo-dev mailing list http://thread.gmane.org/gmane.linux.gentoo.devel/87881/focus=87905.

Save for inheriting the old eclass, the ebuild is compatible with the new eclass.
I've digested it, and included the updated Manifest file in this commit.
The ebuild now works again; it successfully retrieves the source from GitHub, builds and installs cleanly.