configure.ac: refine doxygen version test
configure.ac: refine doxygen version test

Sciumo/GeographicLib,geographiclib/geographiclib,Sciumo/GeographicLib,Sciumo/GeographicLib,Sciumo/GeographicLib,geographiclib/geographiclib,geographiclib/geographiclib,Sciumo/GeographicLib,Sciumo/GeographicLib,Sciumo/GeographicLib,geographiclib/geographiclib,Sciumo/GeographicLib