Make vrocks emit a poison cloud when they flee

dat/data.base

@@ -5465,7 +5465,7 @@ vrock
 	The vrock is one of the weaker forms of demon.  It resembles
 	a cross between a human being and a vulture and does physical
 	damage by biting and by using the claws on both its arms and
-	feet.
+	feet.  It can also release a cloud of noxious gas to hide in.
 wakizashi
 	A wakizashi was used as a samurai's weapon when the katana
 	was unavailable.  When entering a building, a samurai would

doc/fixes37.0

@@ -146,6 +146,7 @@ level compiler creates correct novel with supplied name
 for farlook, describe water in the castle moat and in Juiblex's swamp as moat
 	and as swamp, respectively, rather than just as "water"
 make hezrous emit poison clouds when they move
+make vrocks emit a poison cloud when they flee
 stepping from one type of terrain to another was triggering an unnecessary
 	status update
 make shriekers summon baby purple worms if purple worms would be too tough

include/mondata.h

@@ -29,7 +29,8 @@
 #define resists_ston(mon) \
     ((mon_resistancebits(mon) & MR_STONE) != 0)
 
-#define immune_poisongas(ptr) ((ptr) == &mons[PM_HEZROU])
+#define immune_poisongas(ptr) ((ptr) == &mons[PM_HEZROU]        \
+                               || (ptr) == &mons[PM_VROCK])
 
 #define is_lminion(mon) \
     (is_minion((mon)->data) && mon_aligntyp(mon) == A_LAWFUL)

src/monmove.c

@@ -368,6 +368,12 @@ monflee(
                 pline("%s turns to flee.", Monnam(mtmp));
             }
         }
+
+        if (mtmp->data == &mons[PM_VROCK] && !mtmp->mspec_used) {
+            mtmp->mspec_used = 75 + rn2(25);
+            (void) create_gas_cloud(mtmp->mx, mtmp->my, 5, 8);
+        }
+
         mtmp->mflee = 1;
     }
     /* ignore recently-stepped spaces when made to flee */