Create an empty paniclog file during playground creation, so that it
starts with the same permissions as other writeable files. Without this,
it's liable to end up being owned by the first random user who triggers
a panic or impossibility rather than by the playground owner and probably
wouldn't be writable by any other user.
Instead of adding a new artifact.h to pray.c, remove the existing
ones from attrib.c, invent.c, and mkobj.c. This also updates the Unix
and VMS editions of Makefile.src; having stale dependencies in those
for other ports could cause unnecessary recompilation but can't break
anything in this case.
Prevent the pardoning of trickery in wizard mode from attempting
to continue when there's no longer any current level. Also prevent
the ZEROCOMP configuration from trying to read from file descriptor -1
in case there're any other places which still let that slip through.
And fix an oddity in the VMS port's error() routine which has gone
unnoticed for years.
Update the instructions, add a dat -> util dependency so that
MMK (freeware clone of DEC's MMS make utility) builds the data files
when necessary, and switch the default compiler to DEC C.
