fix #K965 - dropped fragile items don't break

when the drop is being caused by encumbrance or punishment triggering
a fall while going down stairs.

Also, remove a couple instances of 'if (obj==GOLD) contexl.botl=TRUE'
when dropping gold.  They were held over from the obsolete !GOLDOBJ
configuration.  Both are immediately followed by freeinv() which
calls freeinv_core() whichs starts off by setting the botl flag when
taking gold out of inventory.

src/dothrow.c

@@ -440,7 +440,7 @@ boolean verbose;
 }
 
 /* Object hits floor at hero's feet.
-   Called from drop(), throwit(), hold_another_object(). */
+   Called from drop(), throwit(), hold_another_object(), litter(). */
 void
 hitfloor(obj, verbosely)
 struct obj *obj;