Fix: Setting cursor to semitransparent objects will fail because of clip
alpha, added option when drawing depth to disable alpha clip override.
We use that in texture paint cursor now. Not too common but may be
useful for people dealing with cloning plugins.

Reported by kgeogeo on irc, thanks.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55363 954f8c5b-7b00-dc11-b283-0030488c597c