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.
proot: remove self.stdenv.lib
Merge remote-tracking branch 'nixos/master' into proot

Conflicts:
	pkgs/tools/system/proot/default.nix
new package: svg2tikz
Add license for svg2tikz
pharo-vm: Add dependency to cairo
thrift builds on darwin
jq builds on darwin
ansible: update from 1.7.1 to 1.7.2
apg: update from 2.2.3 to 2.3.0b
asio: update from 1.10.2 to 1.10.4
Merge pull request #4381 from khumba/claws-mail

New packages: claws-mail-3.10.1, libetpan-1.5.
Merge pull request #4443 from flazz/master

jq & thrift build on darwin
Merge pull request #4439 from DamienCassou/pharo-vm-with-cairo

pharo-vm: Add dependency to cairo
Merge pull request #4423 from FlorentBecker/svg2tikz

new package: svg2tikz
rtorrent-git: new package
Merge pull request #4412 from wavewave/proot

proot: remove self.stdenv.lib
coq_HEAD: Update
Merge branch 'master' into t/hakyll