compiler/deforest.m:
Don't push goals that may have output variables into semidet conjunctions,
since that turns them into nondet conjunctions, leading to determinism
errors.
tests/hard_coded/bug392.{m,exp}:
A tougher version of the mantis test case.
tests/hard_coded/Mmakefile:
tests/hard_coded/Mercury.options:
Enable the new test case, and run it with the options that used to
tickle the bug.
