Rewrite more refs for epilogue vectorization

The following makes sure to rewrite all gather/scatter detected by
dataref analysis plus stmts classified as VMAT_GATHER_SCATTER.  Maybe
we need to rewrite all refs, the following covers the cases I've
run into now.

	* tree-vect-loop.cc (update_epilogue_loop_vinfo): Rewrite
	both STMT_VINFO_GATHER_SCATTER_P and VMAT_GATHER_SCATTER
	stmt refs.