title: pysvn with svn+ssh
body: <p>I'm working with pysvn, and I'm trying to find a decent way to handle repositories that are only accessible via svn+ssh. Obviously SSH keys make this all incredibly easy, but I can't guarantee the end user will be using an SSH key. This also has to be able to run without user interaction, because it's going to be doing some svn log parsing.</p>
  
  <p>The big issue is that, with svn+ssh an interactive prompt is popped up for authentication. Obviously I'd like to be able to have pysvn automatically login with a set of given credentials, but set_default_username and set_default_password aren't doing me any good in that respect. If I can't have that, I'd at least like to able to just fail out, and log a message to tell the user to setup an SSH key. However, set_interactive seems to have no bearing on this either, and I'm still prompted for a password with client.log('svn+ssh://path'). </p>
  
  <p>Any thoughts on how to tackle this issue? Is it even really possible to handle this without SSH keys, since it's SSH that's throwing the prompts?</p>