SDL2: some improvements to the expression.

Based on comments in the pull request from @edolstra and @peti. I also added
missing metadata, setting myself as maintainer.
Fix sha256 hash of disnix
grsecurity: Update to 2.9.1-3.2.52-201311021628
paxctl: New package

A tool for controlling PaX flags on a per binary basis.
gradm: New package

grsecurity's RBAC administration utility.
firefox: Add support for grsecurity
chromium: Add support for grsecurity