* sftp: support for external SSH command and host verfication improvements
- removed custom parsing of hostnames and verification and replaced with
standard 'knownhosts' implementation.
- added option to launch external SSH command which supports
aliases, agent, etc.
NOTE, we're still not supporting any cases where password needs to be
entered on the command line, since that would be incompatible with
the UI which uses client-server model.
Fixes#500Fixes#414
* site: updated SFTP repository connection instructions
Fixes#590
d0d6ac4767
