Added bzr and subversion as optdepends.

Also updated the descriptions based on the descriptions for the various source control systems (that are somewhat random in how they describe themselves, in terms of where they put the focus).



git-svn-id: file:///srv/repos/svn-community/svn@108205 9fca08f4-af9d-4005-b8df-a31f2cc04f65