git-svn: improve repository URL matching when following parents

This way we can avoid the spawning of a new SVN::Ra session by
reusing the existing one.

The most problematic issue is that some svn servers disallow
too many connections from a single IP, so this will allow
git-svn to fetch from those repositories with a higher success
rate by using fewer connections.

This sometimes showed up as a new (and redundant)
[svn-remote "$parent_refname"] entry in $GIT_DIR/svn/.metadata.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-svn.perl

@@ -2229,7 +2229,12 @@ sub find_parent_branch {
 		# just grow a tail if we're not unique enough :x
 		$ref_id .= '-' while find_ref($ref_id);
 		print STDERR "Initializing parent: $ref_id\n";
-		$gs = Git::SVN->init($new_url, '', $ref_id, $ref_id, 1);
+		my ($u, $p) = ($new_url, '');
+		if ($u =~ s#^\Q$url\E(/|$)##) {
+			$p = $u;
+			$u = $url;
+		}
+		$gs = Git::SVN->init($u, $p, $self->{repo_id}, $ref_id, 1);
 	}
 	my ($r0, $parent) = $gs->find_rev_before($r, 1);
 	if (!defined $r0 || !defined $parent) {