svnrepo: change svnurl to not use self.svn Before this patch, svnremoterepo uses self.svn.svn_url to answer svnurl. Accessing svnremoterepo.svn will create an svn ra object, which can be expensive because it involves network i/o. This patch changes it to use self.svnauth, which is a local operation. It speeds up "hg svn info" a lot. The old behavior is hard to test since instantiating a svn ra object requires a real URL. The change does not seem worth to set up SSH and HTTP servers to test. Therefore the tests are added only for the new behavior.