* Similarly to what was done in revision r16104 for vg_perf, have a way
to append to predefined vg_regtest outer args, rather than only be able
to replace them.
* increase the num callers for outer tool to 40.
(This is in preparation of a future commit, that will allow outer tool
to append the inner guest stack trace to reported errors in the inner)
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@16133