Merge swf files

This is meant to solve the eternal "preloader starts at 80% problem" caused by exporting assets in the first frame.
Prepare your movie:

all jumps in the main scene should be relative, like nextframe(), prevframe(), gotoAndPlay(_currentframe+n) or use frame labels
there should be no common assets for the preloader and the main scene. In particular, if a font is embedded to show percentages, this font must not appear in the main movie.
Split your movie into two separate ones for the preloader and the main scene. If you have items exported from the library, make sure to delete them in the part that does not need it.
add a blank frame at the end of the preloader.
publish both parts as swf