[libvirt] libvirt 0.5.1 tag missing in git repo: just applied manually

FYI, Itamar Heim noticed that the LIBVIRT_0_5_1 tag, while in CVS, was not in the git repository (thanks, Itamar). I have a vague recollection that git cvsimport creates certain tags lazily (like only once there is something on a branch) but I have manually applied and pushed this particular tag, nonetheless.