sync-trees: drop -X and retry if -X fails
sync-trees: drop -X and retry if -X fails

It appears that rsync may fail if -X is specified and the filesystem
doesn't support xattrs.

Thanks to Greg Troxel for reporting the problem and helping test the
solution.

Signed-off-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>
Tested-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>

gevaerts/bup,ToxicFrog/bup,ToxicFrog/bup,ToxicFrog/bup,gevaerts/bup,ToxicFrog/bup,gevaerts/bup,gevaerts/bup,ToxicFrog/bup,gevaerts/bup