Clearing walk_to and its variants

[Generaldonothing]

(Sort of fits on code discussion)
If you are using walk_to or it's variants, to prevent GC issues the walk_to must be cleared on a destroy(). To do this, set walk_to(src,0) (or it's variants) in a destroy proc. If you do not do this, the walk_to will cause a ref to be held an a GC fail. 
These GC issues create a significant number of false positives and are easy to fix. Plenty of files need updating to include this as well, it's a good place to start for new contributors.