* Add a trigger for fc-cache.
* Add a trigger to (un)register users/groups. Currently packages that
  require user/groups use custom INSTALL/REMOVE scripts, which adds
  a lot of duplicated work.
* Require exact versions of dependencies, not greater or equal than.
  This is required for kernel modules, i.e aufs2-kmod.
* Support external remote patches.
* Add the following packages: mercurial, vala.
