development of version 6.0
only a single overlaydir (as root) possible

Will add group support for dirs under overlay/ later
scan relevant group subdirs under overlay/

The subdirs have order of importance (as groups always have, in
synctool)
renamed groupnum to "importance"

Easier to understand code
shorter statements are easier to read

code improvement
added TODO remark
this was already checked
easier to understand code
this was already checked
this was already checked
this was already checked
this was already checked
easier to understand code
additions to commit b44153d
also show the passed ssh options
same code style as in synctool_scp.py
added a tempdir for synctool_master
rsync only relevant subdirs

This enables group-specific overlay dirs
include remark about managing the master itself with synctool
just recoding