Buildbot work

[Nick Schermer]

I've been playing with the buildbot setup we have running on one of
the server, here a summary of the changes:

* To make maintenance a bit lower, I dropped the Lunar bot and the
main system runs Arch, which has a buildbot package. This machine is
also the first buildslave (x86_64) to drop one vm.
* Debian Squeeze bot for i686 (new gtk deps for 4.10)
* License check script runs on one of the slaves, previously
Yves-Alexis bothered us with that ;-).
* Some packages trigger other builds, so 4util -> xfconf -> 4ui...
Hopefully this will make api breaks easier to spot.
* Compile warnings are separately logged (useful for gtk-doc warning
for example), once we have a proper ignore file i can make the build
yellow too, so we easily spot missing code comments.
* Linux slaves use ccache.
* Working on a FreeBSD builder. Partly working...

Still some things to do:

* Hopefully the FreeBSD bot can compile with clang/llvm.
* Trigger builds on git commits.
* Need to work a bit on the build priorities.

Any other suggestions?

Nick