Get rid of the BRUSH_FIXED_TEX flag, use mapping modes instead. Version
patched all previous texture paint brushes to use tiled mapping since
mappping is now shared between 2d and 3d painting.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53846 954f8c5b-7b00-dc11-b283-0030488c597c