Fix retracting spikes dealing typeless damage instead of spike damage.

src/info.c

@@ -7974,7 +7974,7 @@ mobjinfo_t mobjinfo[NUMMOBJTYPES] =
 		8*FRACUNIT,     // radius
 		32*FRACUNIT,    // height
 		0,              // display offset
-		4,              // mass
+		DMG_SPIKE,      // mass
 		0,              // damage
 		sfx_None,       // activesound
 		MF_NOBLOCKMAP|MF_SCENERY|MF_NOCLIPHEIGHT,  // flags
@@ -8001,7 +8001,7 @@ mobjinfo_t mobjinfo[NUMMOBJTYPES] =
 		16*FRACUNIT,    // radius
 		14*FRACUNIT,    // height
 		0,              // display offset
-		4,              // mass
+		DMG_SPIKE,      // mass
 		0,              // damage
 		sfx_None,       // activesound
 		MF_NOBLOCKMAP|MF_NOGRAVITY|MF_SCENERY|MF_NOCLIPHEIGHT|MF_PAPERCOLLISION,  // flags

src/p_map.c

@@ -1156,7 +1156,7 @@ static boolean PIT_CheckThing(mobj_t *thing)
 		else
 			thing->z = tmthing->z + tmthing->height + FixedMul(FRACUNIT, tmthing->scale);
 		if (thing->flags & MF_SHOOTABLE)
-			P_DamageMobj(thing, tmthing, tmthing, 1, 0);
+			P_DamageMobj(thing, tmthing, tmthing, 1, DMG_SPIKE);
 		return true;
 	}