Fixes ArcticaProject/nx-libs#250.

version.def and date.def also will be no longer created

  This feature copies the way how X.Org version string and number
  are propagated at build time.

  First use case: if people start nxagent, it reports its version number
  on stderr. This is about being human-friendly.

  Second use case: None, so far. But it will now be easy to use
  the NXAGENT_VERSION_STRING in later feature add-ons.

Summary: Imported nx-X11-3.1.0-1.tar.gz
Keywords:

Imported nx-X11-3.1.0-1.tar.gz
into Git repository