Instrument

This PR adds the ability to generate instrumented versions of SWF files that print out frame information. This is accomplished using `swfmill` and `xsltproc`:

`swf` -> {swfmill swf2xml} -> `xml` -> `xsltproc utils/instrument-swf.xslt` -> `xml` -> {swfmill xml2swf} -> `swf`.

I've tried this out on some larger files and it seems to work pretty well. Using this we should be able to generate trace output for more complicated ref tests, like games and such. Maybe we can just compare the first few hundred messages before any interactivity happens.

The XSLT transform emits `R frameNumber` for root frames, and `S spriteObjectID frameNumber` for sprites.