Clean up confusion about VG_(args_the_exename) which was believed to
possibly be NULL in several places. Nowadays, VG_(ii_create_image) will
terminate the process if VG_(args_the_exename) is NULL.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14323 a5019735-40e9-0310-863c-91ae7b9d1cf9