fix github issue #531 - genderless corpses

Dead monsters that had traits saved with the corpse would revive as
the same gender, but ordinary corpses revived with random gender so
could be different from before they got killed.

Since corpses of monsters lacked gender, those for monsters with
gender-specific names were described by the neuter name.

This is a fairly big change for a fairly minor problem and needs a
lot more testing.

Fixes #531

src/mkobj.c

@@ -1520,7 +1520,9 @@ mkcorpstat(
     } else {
         otmp = mksobj_at(objtype, x, y, init, FALSE);
     }
-    otmp->norevive = g.mkcorpstat_norevive;
+    /* record gender and 'historic statue' in overloaded enchantment field */
+    otmp->spe = (corpstatflags & CORPSTAT_SPE_VAL);
+    otmp->norevive = g.mkcorpstat_norevive; /* via envrmt rather than flags */
 
     /* when 'mtmp' is non-null save the monster's details with the
        corpse or statue; it will also force the 'ptr' override below */
@@ -1685,10 +1687,10 @@ mk_tt_object(
    never returns Null */
 struct obj *
 mk_named_object(
-int objtype, /* CORPSE or STATUE */
-struct permonst *ptr,
-int x, int y,
-const char *nm)
+    int objtype, /* CORPSE or STATUE */
+    struct permonst *ptr,
+    int x, int y,
+    const char *nm)
 {
     struct obj *otmp;
     unsigned corpstatflags = (objtype != STATUE) ? CORPSTAT_INIT