Better detect missing targets in external projects.


git-svn-id: http://sbuild.tototec.de/svn/sbuild/trunk@408 024a02f7-42f7-40fc-9f58-65666d1f2450
Also generate docbook.


git-svn-id: http://sbuild.tototec.de/svn/sbuild/trunk@409 024a02f7-42f7-40fc-9f58-65666d1f2450