Correct libvtv obstack use

Fixes a compile error with both old and new obstacks due to
obstack_chunk_free having the wrong signature.  Also, setting chunk
size and alignment before obstack_init is pointless since they are
overwritten.

	* vtv_malloc.cc (obstack_chunk_free): Correct param type.
	(__vtv_malloc_init): Use obstack_specify_allocation.

From-SVN: r229985