kick/joust monster positioning (trunk only)

From a 7.5 year old news posting (with a reply by Kevin Hugo speaking
on behalf of slash'em...):  when a monster "nimbly jumps to evade" hero's
kick, it can pass through walls and grid bugs can jump off their grid.
Likewise when a joust or staggering blow knocks a monster back, it could
move grid bugs diagonally.  This fixes both cases.

     Offhand I can't think of any other non-standard movement situations
which might need similar handling, but it wouldn't surprise me if there
are some.  Leashed movement is close but I don't think maybe_mnexto helps.

src/dothrow.c

@@ -724,6 +724,8 @@ mhurtle(mon, dx, dy, range)
     dx = sgn(dx);
     dy = sgn(dy);
     if(!range || (!dx && !dy)) return; /* paranoia */
+    /* don't let grid bugs be hurtled diagonally */
+    if (dx && dy && NODIAG(monsndx(mon->data))) return;
 
 	/* Send the monster along the path */
 	mc.x = mon->mx;