fix issue #332 - mon vs mon double hit message

One monster hitting another with an artifact within the hero's view
gave "<Mon1> swings his <Artifact> at <Mon2>." followed either by
"<Mon1> misses <Mon2>." _or_ the two messages "<Mon1> hits <Mon2>."
and "The <Artifact> hits <Mon2>."  Defer the <Mon1> hits <Mon2> one
when Mon1 is using an artifact and only deliver it if there is no
artifact hit message.

Tested but not exhaustively so....

Fixes #332

doc/fixes37.0

@@ -163,6 +163,7 @@ if riding or levitating, hero could apply bullwhip downward to pull up things
 some monster code was checking whether pets or engulfers were eating green
 	slime by checking for green slime corpse instead of glob
 change light radius of stack of candles to square root
+could get redundate "mon hits other-mon" messages when mon wields an artifact
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository

src/mhitm.c

@@ -557,6 +557,7 @@ int dieroll;
             char magr_name[BUFSZ];
 
             Strcpy(magr_name, Monnam(magr));
+            buf[0] = '\0';
             switch (mattk->aatyp) {
             case AT_BITE:
                 Sprintf(buf, "%s bites", magr_name);
@@ -580,9 +581,12 @@ int dieroll;
                 }
                 /*FALLTHRU*/
             default:
-                Sprintf(buf, "%s hits", magr_name);
+                if (!weaponhit || !mwep || !mwep->oartifact)
+                    Sprintf(buf, "%s hits", magr_name);
+                break;
             }
-            pline("%s %s.", buf, mon_nam_too(mdef, magr));
+            if (*buf)
+                pline("%s %s.", buf, mon_nam_too(mdef, magr));
 
             if (mon_hates_silver(mdef) && silverhit) {
                 char *mdef_name = mon_nam_too(mdef, magr);
@@ -967,8 +971,18 @@ int dieroll;
             if (tmp < 1) /* is this necessary?  mhitu.c has it... */
                 tmp = 1;
             if (mwep->oartifact) {
-                (void) artifact_hit(magr, mdef, mwep, &tmp, dieroll);
-                if (DEADMONSTER(mdef))
+                /* when magr's weapon is an artifact, caller suppressed its
+                   usual 'hit' message in case artifact_hit() delivers one;
+                   now we'll know and might need to deliver skipped message
+                   (note: if there's no message there'll be no auxilliary
+                   damage so the message here isn't coming too late) */
+                if (!artifact_hit(magr, mdef, mwep, &tmp, dieroll))
+                    pline("%s hits %s.", Monnam(magr),
+                          mon_nam_too(mdef, magr));
+                /* artifact_hit updates 'tmp' but doesn't inflict any
+                   damage; however, it might cause carried items to be
+                   destroyed and they might do so */
+               if (DEADMONSTER(mdef))
                     return (MM_DEF_DIED
                             | (grow_up(magr, mdef) ? 0 : MM_AGR_DIED));
             }

src/uhitm.c

@@ -808,6 +808,9 @@ int dieroll;
 
                 if (obj->oartifact
                     && artifact_hit(&g.youmonst, mon, obj, &tmp, dieroll)) {
+                    /* artifact_hit updates 'tmp' but doesn't inflict any
+                       damage; however, it might cause carried items to be
+                       destroyed and they might do so */
                     if (DEADMONSTER(mon)) /* artifact killed monster */
                         return FALSE;
                     if (tmp == 0)