Fixes#177
The monst struct has 'mintrinsics' field which attempts to handle
both mon->data->mresists and extrinsics supplied by worn armor, but
polymorph/shape-change was clobbering the extrinsics side of things.
Potentially fixing that by changing newcham() to use set_mon_data(...,1)
instead of (...,0) solved that but exposed two other bugs. Intrinsics
from the old form carried over to the new form along with extrinsics
from worn armor, and update_mon_intrinsics() for armor being destroyed
or dropped only worked as intended if the armor->owornmask was cleared
beforehand--some places were clearing it after, so extrinsics from worn
gear could persist even after that gear was gone.
So, fixing the set_mon_data() call in newcham() was a no go. This
fixes update_mon_intrinsics() and adopts the suggested code from
github pull request #177 to have mon->mintrinsics only handle worn
gear instead of trying to overload innate intrinsics with that. This
is a superset of that; the flag argument to set_mon_data() is gone
and mon->mintrinsics has been renamed mon->mextrinsics. (The routine
update_mon_intrinsics() ought to be renamed too, but I didn't do that.)
a6ff7210be