add an RPM macro to make use of it in spec files

v2: support filenames with spaces in %fdupes macro
Date: Thu Sep  5 11:57:24 UTC 2007
Author: Werner Fink <werner@suse.com>
Fixes: https://bugzilla.novell.com/show_bug.cgi?id=307727

v3: do not hardlink empty files in %fdupes macro
Date: Thu Sep  6 18:41:37 CEST 2007
Author: Michael Schröder <mls@suse.de>

v4: add an option to sort duplicate files by name
Date: Tue Apr 29 19:12:48 CEST 2014
Author: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Improve Makefile for openSUSE.