Allow marking licenses as unfree

This allows licenses like the Amazon Software License to be identified
properly while still preventing packages with those licenses from
being distributed in the Nixpkgs/NixOS channels.
Make the license shortName attribute equal to the license attribute name

I.e. lib.licenses.<foo>.shortName == "<foo>". The SPDX identifier (if
known) is kept in lib.licenses.<license>.spdxId.
Provide more SPDX IDs
Merge pull request #4838 from abbradar/ssmtp-root

Add 'root' option to ssmtp
gst-plugins-bad: enable gl plugin (close #4763)
findTarballs: Take nullglob into account
Die tabs die
findTarball: Handle pipefail

It was failing because the bash subshell died with SIGPIPE, which is
no longer ignored.

http://hydra.nixos.org/build/16766452
emacs-idris-mode: upgrade to 0.9.15
new package: swaks, a command line SMTP tool
opkg-utils: new package

Helper scripts for use with the opkg package manager.

Upstream doesn't do releases it seems, so I'm packaging the latest git
version.
Update PhantomJS; should also fix remarkjs
Readd BtrFS-progs 3.16 for snapper build
perl-Net-CIDR: new package

Expression is generated with nix-generate-from-cpan. Then I added
platforms and maintainers.
munin: add missing dependency on 'NetCIDR'

Fixes

  munin-node[30100]: Can't locate Net/CIDR.pm in @INC (@INC contains: [...])

when using the 'cidr_allow' configuration directive.
Haskell - added package unification-fd
Merge pull request #4848 from meditans/add-haskell-unification-fd

Haskell - added package unification-fd
add duperemove: btrfs deduplication tool
Add tessel: cli tools and node libs for tessel.io devices
scribus: update from 1.4.3 to 1.4.4