Cleanup remaining modules on loadexec.
Clear module text and bss on unload.

Text is set to break instructions, data/bss to -1.  Matches results on a
PSP.
Return NOT_YET_LINKED for unlinked module funcs.
Warn on exports from syslib.

They don't seem to hook up properly on hardware by the module name.
Return an error code when module load fails.

If we're out of memory, we need to tell the game, of course.