where the error occurred.
Note that line numbers are still not stored in the hlds yet, so
we need to do some more work so that the typechecker, etc. can also
report line numbers.
Lots of bug fixes for make_hlds.nl.
A couple of bug fixes for hlds.nl.
Did some optimization of memory usage: added io__gc_call to io.nl
and used it in prog_io.nl and module.nl. Rewrote the main loop
of prog_io to take maximum advantage of manual garbage collection.
Started working on typecheck.nl.