unlock door spell and some map suggestions

[Tero Kivinen <kivinen@joker.cs.hut.fi>]

Gregor Schmid writes:
> how about a new spell: Unlock door
> Will only work with standard doors, not with those that need special
> keys. Should be low level (say 2) but expensive (~ 10 sp).
> The reason is that a low level mage can hack on those doors for a long
> time (there seems to be a lack of keys on some maps recently).
> If someones would like to implement it, pleas do.

I already implemented this for some old version, but I haven't had
time to patch the code to new version. I also included "lock door" and
"undoor" spells. The unlock door works so it will remove 500 hitpoins
from door and raise its ac by 10. Lock will do the reverse (add 500
hps and lower its ac by 10). Undoor will just remove the door. They
only worked for normal doors, not LOCKED_DOORS or gates etc. 

I will try to patch them to current version and send patches, but it
may take some time (I have lots of work to do currently).
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