testbench: clean up smartmatch warning

Apparently that feature of Perl 5.10.1 was too smart for its own good. So
let's not use an experimental feature here.
testbench: add env parameter to ProcessModule, test for it

Also, ->close now requires a true "force" parameter to SIGINT the child
process. Mung::Loop was modified to always provide that. This change allows
testing of Mung::ProcessModule without always killing the calling make
process.
testbench: change ProcessModule to use fork and exec

Instead of a simple IO::File style pipe. This seems to work just fine, and
lets us kill exactly just the child process in ->close. This also removes the
now-unnecessary "force" parameter therefrom.
make toplevel qcheck target at least somewhat useful
testbench: forkserv: don't convert thread numbers to sp->threads offsets

That scheme is on its way out.