Disable exec symlink resolution for PostgreSQL 9.2

When building PostgreSQL with plugins under NixOS, NixOS will create a
postgresql-and-plugins directory which symlinks PostgreSQL and all the plugins
into a single directory. Unfortunately, the plugins will not actually be usable
by PostgreSQL because it will still try and locate them in the original
PostgreSQL share directory, not postgresql-and-plugins.

In this commit, I have patched resolve_symlinks to always return success, which
matches the behavior if HAVE_READLINK is false (so presumably invalid paths are
never passed to this function).
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.
php54: add pcntl option
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
libedit: add FreeBSD support
Improve description of the users.extraUsers.*.description option

Fixes NixOS/nixos#278.
Generate manual for i686-linux as well as x86_64-linux
haskell-OpenGL: update 2.9.x branch to version 2.9.1.0
haskell-gloss: update to version 1.8.1.1
haskell-xmobar: update to version 0.19
haskell-HDBC-postgresql: update to version 2.3.2.2
haskell-blaze-builder: update to version 0.3.2.0
haskell-constraints: update to version 0.3.4.2
haskell-fclabels: update to version 2.0.0.2
haskell-feed: update to version 0.3.9.2
haskell-hexpat: update to version 0.20.4
haskell-hslua: update to version 0.3.8
haskell-intervals: update to version 0.3