More aggressive fix for *default-hs*, and miscellaneous tweaks for ACL2(hp).

Various mods now prevent _some_ ACL2(hp) regression errors.  However,
I still get "Not owner of hash table" in some book certification
attempts for ACL2(hp), even when *default-hs* is introduced with
defvar in parallel-raw.lisp before the definition of
consume-work-on-work-queue-when-there.  I spent quite some time today
trying to figure out why we still get that error, and got virtually
nowhere, though from the debugger I can see that it's from
hl-hspace-hons-get.  Since ACL2(hp) is labeled "experimental" and I
have other things to do, I'm moving on; besides, I think it's been a
long time since an ACL2(hp) regression passed.  If someone cares to
deal with that, great!