memcheck/tests/Makefile.am include filter_dw4 in dist_noinst_SCRIPTS.

The fix for BZ#331254 (r13814) added filter_dw4.
Make sure it is always included in the dist.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13825 a5019735-40e9-0310-863c-91ae7b9d1cf9