Use BOOST_SPIRIT_NO_PREDEFINED_TERMINALS

This helps very slightly with compile times of cpp files that include headers that use `
#include <boost/spirit/include/qi.hpp>`. Unfortunately it has no measurable impact on the overall compile time of Mapnik. I presume this is because most all cpp files which include `qi.hpp` end up requiring way more compile time effort due to compiling grammars and template instanciations. Nevertheless @djowel has said [here](http://boost.2283326.n4.nabble.com/qi-hpp-include-compile-time-hit-tp3466042p3467731.html) this is best practice for boost >= 1.47 so I think we should go with it.