magic cancellation and Protection (trunk only)

magic cancellation and Protection (trunk only)

     Magic cancellation comes from some types of worn armor and has a
value of 0 through 3.  A non-zero value guards against some forms of
monster magic attacks (most notably, level drain by vampires and wraiths
and lycanthropy from werecritter bites).  This reduces the effectiveness
of mc a moderate amount (the new values happen to be the same as those
adopted by the Spork variant):
 chance to block various touch effects
  mc  old     new
   1  34.67%  30%
   2  67.33%  60%
   3  98%     90%

    This also makes the Protection intrinsic (strictly speaking, extrinsic)
be the only way to attain an mc factor of 3.  Cloak of protection is the
only way to get mc 3 from a single item.  Otherwise you need an mc 2 item
and a ring of protection (or one of the recently modified quest artifacts).

     Cancellation factor for elven and dwarvish mithril coats and for
robes and oilskin cloaks is reduced from 3 to 2; for elven cloak and
cloak of magic resistance from 3 to 1 (play balance; they're valuable
even without magic cancellation); for dwarven and orcish cloaks and
clocks of invisibility and displacement and for cornuthaum (wizard hat)
from 2 to 1.  Plate mail and crystal plate mail stay at 2.  A variety of
suits which were at 0 are increased to 1; leather jacket and dragon
scales/scale mail stay at 0 (the latter for play balance rather than for
the amount of your body that's covered).

     Having extrinsic protection will increase mc by 1 (unless it's
already 3).  That's obtained by wearing a cloak of protection (where the
increase is redundant), a ring (or two) of protection (even if conferring
a negative AC amount), or wearing the Mitre of Holiness or wielding the
Tsurugi of Muramasa.  Having multiple sources doesn't make the benefit
cumulative; it's just +1.

     Intrinsic protection (bought from priest, gained from prayer, gained
from eating rings of protection while polymorphed into metallivore, or
temporary while spell of protection is active) doesn't increase mc from
armor but does provide minimum mc 1 instead of naked 0 (play balance
again; buying it is too easy to let it increase mc 1 or 2 to 2 or 3).
(Extrinsic protection is a superset; its +1 bonus also increases 0 to 1.)

    TODO: add an amulet of protection so player has another option for
extrinsic protection.