message: extract strings should work using python3
diff: @@ -52,7 +52,7 @@ files = glob.glob('src/*.cpp') + glob.glob('src/*.h')
  child = Popen(['xgettext','--output=-','-n','--keyword=_'] + files, stdout=PIPE)
  (out, err) = child.communicate()
  -messages = parse_po(out)
  +messages = parse_po(str(out))
  f = open(OUT_CPP, 'w')
  f.write("""#include <QtGlobal>
  