Don't inverse detected monsters, remove use_inverse option

Using inverse/reverse video for detected monsters was ugly, and the only
reason for the use_inverse option.  I'd used that option previously for
some bar drawing stuff because I thought I needed to, but just now I
realized that A_REVERSE is used freely in other places, so there's no
need for it anymore.
Add new #tip command to empty container contents onto the floor

A container in your inventory or on the floor beneath you can now have
its contents emptied to floor beneath you by tipping it.  This can be
done even with stuck hands (two-handers are no longer verboten in
Gehennom!), or if you have no limbs.

The code is loosely based on code from GruntHack, but it uses
UnNetHack's dump_container, extending it for cursed bags of holding.
This code handles locked containers, bags of tricks, burden, levitation,
sinks, altars and engulfing.

Known bug in related code: Exploding bags of holding in UnNetHack will
bypass engulfing monsters, and won't damage them.