Major Description
Here are my changes to the existing code to add SSH support and align with the existing SFTP support. The files are based on svn revision 463.
I've added several abstract base classes for ssh connection handling. I added SshCache support for SFTP and added support for handling URLs inside the patterns (as addition to normal paths).
Oh yeah, and I've also made a small fix in the SFTP repository to honor the overwrite flag (which was totally ignored before). Hope that was ok.
I've also added support for public key files. They can only be set via attributes and not via url, but that should be ok, because the keyfiles are not host specific and the same key can be used on several hosts. I've also included your prompting mechanism, so also normal passwords can be used pretty conveniently (very nice work btw.). Passwords of key files will be prompted, too, btw.
I've only included javadoc (especially in the resolvers) for documentation, hope this is enough. I would tell the user to choose sftp over ssh, because as a connection oriented protocol it is faster. If sftp is not available or does not work, the fallback should be ssh (which is based on using scp btw.).
Ok, looking forward for the next version so I can use it. 
And thanks for Ivy in general! Great work!