[boost] [mpl] MPL_ASSERT unused variable warning on GCC

The recent change to mpl/assert.hpp on HEAD is causing an unused variable warning on gcc 3.4, 4.0 and 4.1. The megabytes of resulting compiler debug spew is making my xpressive regression tests almost unrunnable. Aleksey? Eg.: ../../../boost/xpressive/detail/static/static.hpp:124: warning: unused variable 'mpl_assertion_in_line_124' -- Eric Niebler Boost Consulting www.boost-consulting.com