chromium: Check sha256 per channel in update.sh.

Until this commit we had a single hash of the whole version response from
omahaproxy. This worked well for not updating unnecessarily but only until one
single channel has a new version available.

Unfortunately the dev version is released quite frequently, so the hash is of no
use at all (we could rather directly fetch everything everytime we execute the
script).

This led to this commit, which adds two methods of caching:

First of all, if a perticular version/channel is already in the previous version
of the sources.nix file, don't download it again.

And the second method is to check if the current sha256 is already downloaded
and reads the corresponding sha256 from the lookup table.

So, this should really help to avoid flooding the download servers and to not
stress impatient users too much.
chromium: Update channels to latest versions.

This removes the now obsolete VHASH line in sources.nix aswell.
Julia: update source revision
nix: Update to latest unstable version
Update coq to 8.4
Merge branch 'master' of https://github.com/NixOS/nixpkgs
Correcting filename.
Fixing configure patch for coq 8.3.
virtualbox: Use Linux's kbuild to build modules.

Don't rely on VirtualBox's in-tree build scripts to set include paths correctly
and use the official way of the Linux kernel to build the modules. That way we
don't need to make ugly symlinks in the kernel tree or heavily patch VirtualBox.
virtualbox: Fix wrong path when recursing modules.

The for loop didn't find $curdir, because it was set _after_ the directory has
been changed. The variable is now called $srcroot and is set before the
installPhase is changing directories.
virtualbox: Set depmod path to /do_not_use_depmod.

The scripts/depmod.sh checks whether the path in $DEPMOD is executable and only
executes it if that's the case. So, by setting DEPMOD to "/do_not_use_depmod"
the destination path doesn't exist _and_ thus isn't executable aswell.
virtualbox: Separate modules build and install.

First of all, modules won't install when there is no "make modules" prior to it,
so we're doing this now with a new function called forEachModule, so we can
avoid duplication as much as possible.

In addition this sets $sourcedir to the current directory of the configurePhase,
so we're able to find the source tree later on, after several chdir()s.
virtualbox: Remove redundant NIX_CFLAGS_COMPILE.

The "include/generated" stuff is already added to the search path by the kernel
modules build system, so no need to hack it in like this.
virtualbox: Don't build modules for guests.

We're the host so we don't need the kernel modules for the guest additions, as
they're build with in a separate derivation anyway.
virtualbox: Add symbol versions to all modules.

Copy all symbol versions from the ones generated in the vboxdrv build.
virtualbox: Remove unused variable $srcroot.

Thanks to @shlevy for mentioning this.
gpsbabel: Update to 1.4.3.
Merge branch 'virtualbox-manual-kernel' of github.com:aszlig/nixpkgs

virtualbox: Fix build for manual kernel.

This should fix building VirtualBox against kernels made using the new
manual kernel configuration system.

This has been tested with the standard nixpkgs kernel as well.
slim: Build with ConsoleKit support
gcc 4.5: Update to 4.5.4.