#207 $lib/mpi permits arbitrary MPI evaluation with M2

It's possible to do something similar to the following:

$include $lib/mpi

main
me @ "_/ide" getprop var! pr
me @ "_/ide" "{otell:is a goober!}" setprop
me @ parse_idesc pop
me @ "_/ide" pr @ setprop
;

Obviously the example here is relatively harmless since
it could be done with notify_exclude anyway, but more
malicious code could easily be constructed. Should M2
be able to evaluate arbitrary MPI as the current user?