U550 - grid bug travel

when travelling and polymorphed into a grid bug, don't move diagonally.

doc/fixes34.2

@@ -115,6 +115,7 @@ typos fixed in data.base
 add looting freehand() check to able_to_loot() to prevent opening container
 	only to be told that you can't loot anything
 Schroedinger's Cat could be placed at wrong location when its box is carried
+travel while polymorphed into a grid bug should not move diagonally
 
 
 Platform- and/or Interface-Specific Fixes

src/hack.c

@@ -553,6 +553,9 @@ int mode;
     register struct rm *tmpr = &levl[x][y];
     register struct rm *ust;
 
+    /* no diagonal movement for grid bugs */
+    if (dx && dy && u.umonnum == PM_GRID_BUG) return FALSE;
+
     /*
      *  Check for physical obstacles.  First, the place we are going.
      */