Fix drivers and shape keys not handling subframes / frame mapping properly.

Change Scene.frame_set so that it ensures subframe in range [0,1[ as Blender
expects, otherwise some things like physics point cache lookups don't get
evaluated properly.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54122 954f8c5b-7b00-dc11-b283-0030488c597c