some edit fixes

* fixing edit paste
* fix power of 2 check for corner selection
* fix pasting multiple selections changed target selections
* fixing editdrag: plugging memory leak
* fixing editdrag: proper binding of keys
* fixing editdrag: allow deselecting (by selecting a second time)
* make a little more room for undos (RAM is cheap and maps are big)
* some cleanups

source/src/worldlight.cpp

@@ -362,7 +362,8 @@ void blockpaste(const block &b, int bx, int by, bool light)
             dest->b = tb;
         }
     }
-    remipmore(b);
+    block bb = { bx, by, b.xs, b.ys };
+    remipmore(bb);
 }
 
 void blockpaste(const block &b)