[boost] [units] warnings under msvc

AMDG msvc 8.0 gives the following warnings with /W4: static_rational.hpp line 96 warning 4100: unreferenced formal parameter. T(N)/T(D) should work. conversion.hpp warning 4512: conversion_helper::quantity_conversion_helper assignment operator could not be generated. io.hpp warning 4512 unit_output_helper assignment operator could not be generated io.hpp line 137 warning 4127: conditional expression is constant try if(boost::is_same<Dim,dimensionless_type>()) In Christ, Steven Watanabe