build: do a better job of making up a build number for git
http://bugs.activestate.com/show_bug.cgi?id=101753

(integrated from komodo (trunk) change 83356 by marky)

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@14089 b87d16e7-d29f-4ee1-b5ec-817d645d335f