nixos: Add option services.cron.cronFiles

This allows you to configure extra files that should be appended to your
crontab. Implemented by writing to /etc/crontab when the cron service starts.
Would be nicer to use a cron that supports /etc/cron.d but that would require
us to patch vixie-cron.
update fish shell
traceroute: depends on linux headers.
proot: User-space implementation of chroot, mount --bind and binfmt_misc
Add claws-mail and libetpan.

Adds Nix expressions for claws-mail (http://www.claws-mail.org) and a
dependency that is not already in the tree, libetpan
(http://www.etpan.org/libetpan.html).

The Claws expression has flags for toggling the build of various plugins.
add redmine package
nixos: add redmine service
proot: remove unnecessary phases
Merge branch 'nixos-cronfiles' of git://github.com/rickynils/nixpkgs

nixos: Add option services.cron.cronFiles
Merge pull request #4406 from wavewave/proot

proot: User-space implementation of chroot, mount --bind and binfmt_misc
tornadokick: bump
Add ujson python package
Merge pull request #4409 from iElectric/redmine

Add Redmine package and NixOS Service
Revert "Merge pull request #4406 from wavewave/proot"

This reverts commit 552d1ec8b36515c3de5d660815a521353419bae6, reversing
changes made to 3432414808afa5bdb2019f165365f5b6ff46cf2f.
Document meta.branch
Specify Box2D_2_0_1 branch
Specify meta.branch for pinned celt versions
Specify meta.branch for CLisp-2.44.1
Update Dia
Specify branch for eigen2