git-svn: Abort with an error if 'fetch' parameter is invalid.

Previously, if a config entry looked like this:

         svn-remote.svn.fetch=:refs/heads/whatever

git-svn would silently do nothing if you asked it to "git svn fetch", and
give a strange error if asked to "git svn dcommit".  What it really wants is
a line that looks like this:

	svn-remote.svn.fetch=:refs/remotes/whatever

So we should simply abort if we get the wrong thing.

On the other hand, there's actually no good reason for git-svn to enforce
using the refs/remotes namespace, but the code seems to have hardcoded this
in several places and I'm not brave enough to try to fix it all right now.

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

git-svn.perl

@@ -1420,8 +1420,12 @@ sub read_all_remotes {
 	    svn.useSvmProps/) };
 	$use_svm_props = $use_svm_props eq 'true' if $use_svm_props;
 	foreach (grep { s/^svn-remote\.// } command(qw/config -l/)) {
-		if (m!^(.+)\.fetch=\s*(.*)\s*:\s*refs/remotes/(.+)\s*$!) {
-			my ($remote, $local_ref, $remote_ref) = ($1, $2, $3);
+		if (m!^(.+)\.fetch=\s*(.*)\s*:\s*(.+)\s*$!) {
+			my ($remote, $local_ref, $_remote_ref) = ($1, $2, $3);
+			die("svn-remote.$remote: remote ref '$_remote_ref' "
+			    . "must start with 'refs/remotes/'\n")
+				unless $_remote_ref =~ m{^refs/remotes/(.+)};
+			my $remote_ref = $1;
 			$local_ref =~ s{^/}{};
 			$r->{$remote}->{fetch}->{$local_ref} = $remote_ref;
 			$r->{$remote}->{svm} = {} if $use_svm_props;