I have an enhancement to the current SCP plugin. It needs some polishing and
adding of documentation, but it works well.

1) Added a support for the SCP key authentication.

2) Added an ability to run SCP upload in more concurrent threads. This also
involves changes to the format of specification about source files. My
implementation supports only whole directories including subdirectories, it
doesn't support fileset scanners (their implementation is rather complex).

I'll attach the CVS diff.