[boost] [parameter] increase BOOST_PARAMETER_MAX_ARITY

hi, i've been using boost.parameter extensively with boost.heap and now came to a point, that i need to raise BOOST_PARAMETER_MAX_ARITY to at least 7 in order to be able to compile it. i am planning to merge boost.heap into trunk in the next few days, so i wonder, would it be reasonable to increase the default of this value to e.g. 8 (patch attached)? currently, boost.heap defines BOOST_PARAMETER_MAX_ARITY before including boost/parameter.hpp, but this will break, if boost/parameter.hpp is included before the boost.heap headers. it would be great, if the default would be high enough to compile all boost libraries, or could this cause any issues? thanks, tim