Renamed the debug package to lumail-dbg.

  This fixes the lintian warning.
  Bump Debian standards version to 3.9.4.

  No changes required.
  Reformat to avoid lintian warning on long line.
  Move the -dbg package to have "Priority: extra".
 Move towards hardening the source, via compiler flags.

  This will only be used on the Debian binary packages,
 once released.
  Ignore ./debian/lumail-dbg.

  We've renamed the debug package so this is the new name for
 the previously-ignored directory lumail-debug.