Enable multires bake to level 0

Uses trick with crating simple subdivided mesh with
level 1 and bakes against it.

From quick tests seems to be working correct, more
tests are welcome.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60994 954f8c5b-7b00-dc11-b283-0030488c597c
Code cleanup: remove unused block from multire baker

Mapping from grid on ll 0 was not used and was incorrect
since bmesh merge anyway.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60995 954f8c5b-7b00-dc11-b283-0030488c597c