Fire unload clip event when a movie clip is removed. Added
`ActionType` enum used by `ActionQueue::queue_actions` that
determines the type of action that is running (replaces `is_init`
parameter).
Add DisplayObject::slash_path to get the Flash 4-style slash path
to the clip. This fixes the tellTarget regression test and removes
the superfluous `target_path` from `UpdateContext`.
DisplayObject code no longer has to manage
UpdateContext::active_clip before calling out to children, because
each child still has access to its Gc pointer.
This pushes an extra `undefined` onto the stack to fix underflow in AS2 interface declarations.
It is currently unknown if this is a miscompilation or if some other value is supposed to be there.
# Conflicts:
# core/src/avm1.rs
# core/src/avm1/object.rs