Integrated the code from https://build.opensuse.org/package/show/home:jsmeix/rear1161btrfs2 into mainstream code;
See also https://bugzilla.opensuse.org/show_bug.cgi?id=908854 for full details;
Modifications required for Fedora with the root subvolume; tested on Fedora with success;
more tests are still required for SUSE SLES11, SLES12 and OpenSuse 13.*