A few tweaks:
Use VG_(strdup) instead of VG_(arena_strdup). Likewise for VG_(free).
Avoid memory leak in case ML_(find_executable) is called more than once
(which it currently is not).


git-svn-id: svn://svn.valgrind.org/valgrind/branches/BUF_REMOVAL@14586 a5019735-40e9-0310-863c-91ae7b9d1cf9