sunsword vs gremlin

The original report complained that gremlins seemed impervious to
Sunsword's light yet a flash from a camera caused them to cry out in pain
despite "The long sword named Sunsword begins to shine brilliantly!"

This commit does two things:
1. A dmg bonus is applied against gremlins using a lit Sunsword.
2. Gremlins will generally avoid the light emitted by Sunsword.
There's a few minor flavor bits thrown in also.

It is understood that this effectively makes Sunsword provide
"gremlin-proofing", but the gremlin myth and Sunsword's characteristic
feature pretty much demand it.

bug 42

src/mondata.c

@@ -312,6 +312,14 @@ register struct permonst *ptr;
                       || (ptr->mlet == S_IMP && ptr != &mons[PM_TENGU]));
 }
 
+/* True if specific monster is especially affected by light-emitting weapons */
+boolean
+mon_hates_light(mon)
+struct monst *mon;
+{
+    return (boolean) (hates_light(mon->data));
+}
+
 /* True iff the type of monster pass through iron bars */
 boolean
 passes_bars(mptr)