support localcall invoking first arg handler, getting/setting behavior props through sprite

[matthewdean]

I'm not sure why it shows 38 commits - I'm just trying to merge 4 commits:

• fix the bytecode index of the sprite member property - there appears to have been a typo where scriptNum was copied and not replaced
• support localcall invocations where the first argument doesn't use the receiver's handler and instead uses the handler of the first arg by the same name. this is similar to the behavior we see in extcall so i refactored this functionality out into a reused method.
• add append built-in
• getting/setting sprite props now checks behaviors

[rvanlaar]

Congrats on getting it working so far.

Regarding the commits, this can happen with a merge. It sounds like what you want is a rebase.