Workaround for textured display with dynamic topology enabled

This will only make object display with proper shape in textured
view, but all materials and textures will be replaced with default
gray color. There's currently no better way to deal with textured
display when dynamic topology enabled because of all UV/tfaces are
clearing when enabling dynamic topology sculpt.

Anyway, better to display gray object with proper lighting in this
case rather than not update object's shape during sculpt.

Proper solution will be possible once CD layer will be preserved
by BMesh log.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53598 954f8c5b-7b00-dc11-b283-0030488c597c