While checking for orphans in automatic mode (xbps-query -O,
xbps-remove -o) there's no need to generate a fulldeptree...
instead we need to iterate against pkgdb until no more orphans
are found.
See https://github.com/void-linux/xbps/issues/156#issuecomment-578473222
Also add some debugging that helped me to catch the issue
easily.
Closes#156