[lmi] [PATCH] Simple fix for yet another clang warning in Boost code

[Vadim Zeitlin]

 Hello,

 I think I haven't built lmi with clang since rate table stuff was added in
4f738399b2a45029ba1535cad186e0e4d5cda67e, but now that I try to do it I'm
getting

        In file included from .../rate_table.cpp:33:
        In file included from .../3rdparty/boost_1_33_1/boost/optional.hpp:15:
        .../3rdparty/boost_1_33_1/boost/optional/optional.hpp:668:34: error: 
unused parameter 'x' [-Werror,-Wunused-parameter]
        bool operator == ( none_t const& x, optional<T> const& y )
                                         ^
        .../3rdparty/boost_1_33_1/boost/optional/optional.hpp:673:33: error: 
unused parameter 'x' [-Werror,-Wunused-parameter]
        bool operator < ( none_t const& x, optional<T> const& y )
                                        ^
        2 errors generated.
        Makefile:4569: recipe for target 'rate_table.o' failed
        make[1]: *** [rate_table.o] Error 1

and the build fails. I don't understand why doesn't g++ give the same
warning because the parameter is clearly unused, but it seems logical that
clang does, so I'd like to fix this by locally disabling this warning for
it as done by https://github.com/vadz/lmi/pull/45

 The only alternative would be to patch Boost headers to remove the
"none_t" parameter name, please let me know if you think this would be
preferable.

 Thanks in advance,
VZ