git-svn: fix commits over svn+ssh://

git-svn: fix commits over svn+ssh://

Once a get_commit_editor has been called from an SVN session, RA
layer operations are not allowed (well, unless you're using
file:// or http(s)://).  So we'll pass an alternate SVN::Ra
object to our editor object for running 'check-path'.

This should fix commits over svnserve (svn:// without ssh, too).

Closes Debian bug #392702, thanks to Pierre Habouzit for
reporting the bug.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>