buildbot: bump to version 0.8.7p1 (latest stable)

* 0.8.7p1 doesn't contain *.info documentation; build 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.
buildroot-slave: new package

Tested with buildbot (master).