[boost] [preprocessor][dmc] improved dmc conformance

Paul, The newest Digital Mars compiler (8.45) appears to pass all the preprocessor tests when the dmc workarounds are removed. (Specifically, I set BOOST_PP_CONFIG_FLAGS() to (0x0000) and removed the 'dmc' directories for good measure; the result is the same if I set BOOST_PP_CONFIG_FLAGS() to BOOST_PP_CONFIG_STRICT()). If you can verify this, you might want to consider removing the workarounds. Since hardly any of Boost compiles on dmc right now (PP being one of the exceptions), there shouldn't be backward compatibility problems. Jonathan