Cosmetics

@stafwag, I ran across convertPgsSub [over on Freecode](http://freecode.com/projects/convertpgssub) and noticed that it happened to perform a task I think I'll have to tackle sometime in the next couple of weeks.  Originally I had just planned to read the script for comprehension, but while doing so I happened to notice a few primarily cosmetic details which were making it a bit challenging to pick out the important bits of logic.

I changed very little functionality (ll(orig). 140-173, which seemed a bit incorrect, possibly some old debug code left in; ll(pull). 181-182, which introduces a new dependency on `grep`'s `-q` switch while getting rid of a call to `cat`), and did not touch any of the core logic.  (I _think_ that can be further cleaned up by replacing `$IndexFile` and `$VideoTracks` with arrays, which should also eliminate the need for the supporting file management code, but I have to read more about `mkvmerge`/`mkvextract` first).

I beg your patience, I'm very new to github and don't yet have a firm grip on the etiquette of pull requests.  Thanks for writing this tool!