This ssh file adaptor relies on sshfs/fuse.  It mounts a remote file system, and
then translates all URLs into local URLs, in that mounted name space, and
operates via the local adaptor.

MacOS:
  FUSE:   http://code.google.com/p/macfuse/
  SSHFS:  http://code.google.com/p/macfuse/wiki/MACFUSE_FS_SSHFS

Linux:
  FUSE:   http://fuse.sourceforge.net/
  SSHFS:  http://fuse.sourceforge.net/sshfs.html

The adaptor mounts the remote file systems into

  ~/.saga/adaptors/ssh/ssh_file/mnt/<unique_id>

Latency for mounting a fs is a <10 seconds (usually about 1).  The
mounts are refcounted, so the last object using the mount is doing the
umount.  (The 'sshfs_keepalive' option determines if the filesystem is
umounted when the respective SAGA object gets destroyed.)