git-svn: Abort with an error if 'fetch' parameter is invalid.
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 <e03ccfb89d416c4697ad6970ce86a92c1c28a78e@gmail.com>
Acked-by: Eric Wong <8c2951295f8292b0c03727bc4652981172298eae@yhbt.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git