Inconsistent/unintended inclusion of io.hpp

[Hans-Andreas Engel <engel@…>]

The following includes of io.hpp (and iostream) are probably unintended, given that they are not included in the other files. It would be nice to remove these (and possibly include io.hpp elsewhere).

$ egrep -r 'iostream|io\.hpp' units | egrep -v '\.svn|(si|cgs)/io\.hpp'
units/systems/angle/revolutions.hpp:#include <boost/units/io.hpp>
units/systems/angle/degrees.hpp:#include <boost/units/io.hpp>
units/systems/angle/gradians.hpp:#include <boost/units/io.hpp>
units/systems/si/area.hpp:#include <iostream>
units/systems/si/area.hpp:#include <boost/units/io.hpp>
units/systems/temperature/fahrenheit.hpp:#include <boost/units/io.hpp>