Merge remote-tracking branch 'origin/2.7' into 2.8

* origin/2.7:
  fix some compiler warnings in libnml
  debian buster packaging: use correct package names for python imaging debs
  let debian/configure specify python-imaging and python-imaging-tk package names
  debian/configure: Debian-testing will become Debian-10
  packaging: don't depend on python-gnome2
  remove unused program halgui
  hy_gy_vfd: fix modbus byte timeout
  mb2hal: add support for libmodbus 3.1.2 and newer