Postscript filter should be included by default

[Jesse]

Binary package hint: tracker

Tracker comes with a handful of filters, some of which even using programs not installed (which is actually fine for most users). Postscript is as popular as PDF, so its filter should be included by default.

I wrote a simple filter using ps2txt after discovering that none of my postscript files appeared in the search results, which is already 3 months after enabling tracker. I wish this wouldn't happen to future users