Don't send retain / release messages in GC mode when copying object pointers into blocks.

blocks_runtime.m

@@ -363,11 +363,15 @@ void _Block_object_assign(void *destAddr, const void *object, const int flags)
 		{
 			fprintf(stderr, "-retain\n");
 			id src = (id)object;
-			id *dst = destAddr;
+			void **dst = destAddr;
+			*dst = src;
+			if (!isGCEnabled)
+			{
 				*dst = [src retain];
 			}
 		}
 	}
+}
 
 /* Similarly a compiler generated dispose helper needs to call back for each
  * field of the byref data structure.  (Currently the implementation only packs
@@ -436,10 +440,13 @@ void _Block_object_dispose(const void *object, const int flags)
 		else if((flags & BLOCK_FIELD_IS_OBJECT) == BLOCK_FIELD_IS_OBJECT)
 		{
 			id src = (id)object;
+			if (!isGCEnabled)
+			{
 				[src release];
 			}
 		}
 	}
+}
 
 
 // Copy a block to the heap if it's still on the stack or increments its retain count.