code cleanup: BLI_array.h's BLI_array_grow_items macro was unmanageable.
moved the main re-alloc logic into a C function.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53910 954f8c5b-7b00-dc11-b283-0030488c597c