Mac HiDPI support:

With the good help from googling, here's code that compiles for
10.6 natively. Will check on 10.7 and 10.8 right after commit.



git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53678 954f8c5b-7b00-dc11-b283-0030488c597c