boost gil narrowing error

[springmeyer]

Need to report this upstream in boost. For now we can workaround with -fpermissive or -Wno-c++11-narrowing as in 64efd5f

/Users/dane/projects/mapnik-packaging/osx/out/build-libc++-x86_64/include/boost/gil/channel_algorithm.hpp:54:85: error: non-type template
      argument evaluates to -1, which cannot be narrowed to type 'unsigned long' [-Wc++11-narrowing]
struct unsigned_integral_max_value : public mpl::integral_c<UnsignedIntegralChannel,-1> {};
                                                                                    ^
/Users/dane/projects/mapnik-packaging/osx/out/build-libc++-x86_64/include/boost/gil/channel_algorithm.hpp:204:19: note: in instantiation of
      template class 'boost::gil::detail::unsigned_integral_max_value<unsigned long>' requested here
        if (src > unsigned_integral_max_value<uintmax_t>::value - div2)
                  ^
1 error generated.

[springmeyer]

looking in the boost trunk sources this appears fixed and reads:

template <typename UnsignedIntegralChannel>
struct unsigned_integral_max_value : public mpl::integral_c<UnsignedIntegralChannel,integer_traits< UnsignedIntegralChannel>::const_max> {};

So, it looks like we can remove the -Wc++11-narrowing flag at boost 1_55 ( presumably the next release)