MovieClip.loadMovie is not implemented and send the correct
variables. NOT tested for _level loading.

We also need to fix GETURL with target load (and I guess with
window target too, which would include extending the browser-standalone program protocol to accept POST)

When calling MovieClip.loadMovie with GET or POST method,
then removing the target movieclip and substituting it with
another one with same name, the expected behaviour is that
the variable sent are the ones of the old movie, not the one,
while the loaded resource will still replace the new one,
not the old movie.

This was tested with the MovieClip.loadMovie method, not
with the GETURL tag, so must test that as well.

To fix this, we'll need movie_root::loadMovie taking
not only a "method" argument, but the actual variables
to send. I added a TODO comment for this in the movie_root::loadMovie method description.

Making automated testing for this will require a running http,
not easy...