buildbot: bump to version 0.8.7p1 (latest stable)

* 0.8.7p1 doesn't contain *.info documentation; use manpage
  instead
* Update meta.description to not contain the package name (redundant)
* 0.8.7p1 only builds with python dateutil==1.5, so that has to be added
  as well

Runtime tested with the buildbot slave that is added in the next commit.
buildbot-slave: new package

Tested with buildbot (master).
linux-3.0: upgrade to 3.0.77
linux-3.4: upgrade to 3.4.44
freicoin: update to 0.0.2
Adding pwnat.
Adding udptunnel

(Fixing a semicolon in pwnat expr too)
Merge pull request #511 from bjornfor/buildbot

Buildbot version bump and add buildbot-slave
added libcello
Merge pull request #512 from dysinger/t/libcello

Add libcello (libcello.org)
Adding Otter theorem prover. The development is frozen, but because of that Otter is considered a very reliable prover from soundness point of view.
Adding pcl. (Also updating flann, reworking vtk)
pwnat: Fix evaluation
Revert Merge x-updates into master due to mesa bloat

See #490 discussion.

This reverts commit 1278859d3167b9f84bfab680d9c8c463adf64a60, reversing
changes made to 0c020c98f9d4f49d5c9907db5f4b35aac7df959b.

Conflicts:
	pkgs/desktops/xfce/core/xfce4-session.nix (take master)
	pkgs/lib/misc.nix (auto)