kde/qt doxyfile tags

[Bernd Pol]

Hi Amilcar,

I appreciate that you did add system library tags to the Doxyfile. I use 
those for months now and found them being of great navigational help.

Yet I think this should not be hard-coded but put in the automake 
machinery. configure has to find out where the tags actually are and 
then append them to the doxyfile.

Have a configure switch for this. It takes notably more time to run 
doxygen with the tag links enabled. Also they introduce a bunch of 
extra error messages. :-(

Bernd