* Factorise code between is_valid_for_client and is_valid_for_valgrind.
* Implement VG_(am_is_valid_for_valgrind)
* Use it in gdbsrv to check accessibility when hostvisibility is activated



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13903 a5019735-40e9-0310-863c-91ae7b9d1cf9