[users] Graphviz plugin config

[Stefan Radman]

Package graphviz 2.8 is missing the plugin configuration file
	%{_libdir}/graphviz/config

Without this file dot reports
	Error: Layout was not done.  Missing layout plugins?

Adding 

  %post 
  %{_bindir}/dot -c

Will fix this problem

Reference: http://www.graphviz.org/bugs/b855.html

Have a nice day
Stefan