Attempt at compiling MilkyTracker, but recent zlib version may have broken it.

There's a zlib version included with milkytracker,
but there's no makefiles for it. I've only included
the header here, but it fails at link-time with
several 'undefined reference' errors, which simply
means it can't find the definitions, e.g. compiled
zlib.
There's bug reports on other package systems although
unfortunately still unresolved.
https://bugs.archlinux.org/task/31324
http://lists.freebsd.org/pipermail/freebsd-ports/2013-March/082180.html
MilkyTracker: fix build, use system zlib and decompressor patch

Also add JACK support
MilkyTracker: Tidy up, sort buildInputs and use the attrPath for the license
Added milkytracker: Compiles and runs.
nixos/nginx: allow to specify which package to use

This enables to override which plugins to include with nginx by allowing to change
nginx package. I also removed webdav option in nginx nixos module, because you
can now specify this by overriding nginx package.
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
qimageblitz: Mark stack as non-executable (patch taken from Gentoo)

This allows applications such as okular and kolourpaint to run in
grsecurity kernels, which disallow executable stacks by default.
grsecurity: Add patch for 3.11.x kernels