helper to nil out instance variables, usefull in dealloc.
helper to assign each instance variable a debug label equal to
its instance variable name.
store observation blocks in an NSHashTable with weak memory configuration,
so now things dealloc properly and we no longer need rmext_on_dealloc.
remove deallocation-related helpers.  they are no longer needed in
rm-extensions, and probably should be avoided if you are using them
elsewhere
bump