sitting in lava and other utraptype sit messages

Several cases in the trap block of code in dosit() were caused by utraptype
being set to values not corresponding to an actual trap.  <Someone>
reported back in 12/02 that the "sitting in lava" killer message could not
occur, but the special-case sit messages for TT_INFLOOR and TT_BURIEDBALL
couldn't occur either.

doc/fixes34.2

@@ -74,6 +74,7 @@ add more calls to update_inventory as the inventory changes
 don't charge for items picked up from monster's interior while swallowed
 choking while eating non-food always called the food "quick snack"
 short swords are not throwing weapons
+several sit-in-trap cases were unreachable
 
 
 Platform- and/or Interface-Specific Fixes

src/sit.c

@@ -68,7 +68,8 @@ dosit()
 	    if (!(Is_box(obj) || objects[obj->otyp].oc_material == CLOTH))
 		pline("It's not very comfortable...");
 
-	} else if ((trap = t_at(u.ux, u.uy)) != 0) {
+	} else if ((trap = t_at(u.ux, u.uy)) != 0 ||
+		   (u.utrap && (u.utraptype >= TT_LAVA))) {
 
 	    if (u.utrap) {
 		exercise(A_WIS, FALSE);	/* you're getting stuck longer */