svn: allow branches outside of refs/remotes

svn: allow branches outside of refs/remotes

It may be convenient for some users to store svn remote tracking
branches outside of the refs/remotes/ heirarchy.

To accomplish this feat, this patch includes the entire path to
the ref in $r->{'refname'} in &read_all_remotes and tries to change
references to this entry so the new value makes sense.

[ew: fixed backwards compatibility, long lines]

Signed-off-by: Adam Brewster <adambrewster@gmail.com>
Signed-off-by: Eric Wong <normalperson@yhbt.net>