hats vs helms

Something from <Someone>'s list:  some messages have hardcoded references
to "helmet" which sound strange when the character is wearing a hat or cap.
helm_simple_name() is comparable to the existing cloak_simple_name().  It
returns "helm" or "hat" depending upon whether the helmet provides the
same protection that yields the assorted repetitions of "fortunately,
you are wearing a hard helmet".  This choice ends up categorizing elven
leather helm as a hat (which I think is ok given that its undiscovered
description is "leather hat"), contrary to <Someone>'s suggestion that the
distinction be made based on whether the helmet was made of cloth.

     I started on this a year and a half ago but didn't commit it.
Unfortunately I don't remember why and haven't done any significant
additional work now--just recovered from some intervening bit rot and
confirmed that the patch as is seems to be working ok (in the trunk; the
branch side has not been tested).  I suspect that I meant to look for
additional helmet messages which could benefit from conditional headgear
description.  (Those "hard helmet" ones don't need it, although they
should perhaps be moved into a common routine instead of being replicated.)

doc/fixes34.4

@@ -62,6 +62,7 @@ incorrect screen display if engulfer gets turned to stone when trying to
 panic on subsequent move if engulfer gets turned to stone and poly'd hero
 	also has attached ball&chain
 give more specific messages when dropping weapons due to slippery fingers
+various helmet messages changed to distinguish between "helm" and "hat"
 
 
 Platform- and/or Interface-Specific Fixes