bmesh speedup: skip free-realloc while running CustomData_bmesh_merge() when nothing is changed (happens quite often that there is nothing to do).


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56614 954f8c5b-7b00-dc11-b283-0030488c597c
bmesh: avoid using BLI_array macros for every face when converting to bmesh, replace with alloca 


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56615 954f8c5b-7b00-dc11-b283-0030488c597c