[boost] [Fusion] another nil issue

I see there was work about 5 months ago to avoid the Obj-C++ nameclash with nil in Boost.Fusion: https://github.com/boostorg/fusion/commit/12d2898287a124ff4b398fd3fff512b6f9... Thanks for that as there are alot of use using boost in this scenario. However, I have found another couple nameclashes that prevented me from linking against Boost.Log in the latest trunk on OS X with clang, when trying this sample code: http://boost-sandbox.sourceforge.net/libs/log/example/doc/tutorial_trivial_f... Attached is the changeset I needed to make to build. Does this seem acceptable to the maintainers? Best, Rich