Fix bug in copy []+y, a. "Hero" no longer leaves a trail.

eg/proto-game.60p

@@ -239,8 +239,14 @@ routine player_logic
         copy [ptr] + y, a
         cmp a, 32
         if z {
-            copy new_pos, pos
             copy 81, [ptr] + y
+
+            copy ^screen, ptr
+            st off, c
+            add ptr, pos
+            copy 32, [ptr] + y
+
+            copy new_pos, pos
         } else {
             // copy game_state_game_over, dispatch_game_state
             trash n

src/sixtypical/analyzer.py

@@ -414,7 +414,10 @@ class Analyzer(object):
 
             # FIXME: this is just to support "copy [foo] + y, a".  consider disallowing `a` as something
             # that can be used in `copy`.  should be using `st` or `ld` instead, probably.
-            if dest != REG_A:
+            if dest == REG_A:
+                context.set_touched(REG_A)
+                context.set_written(REG_A)
+            else:
                 context.set_unmeaningful(REG_A)
 
         elif opcode == 'with-sei':