mods to boost gil

* channel.hpp: svn [17210](https://isrsvn.usurf.usu.edu/trac/isr/changeset/17210#file87), [21296](https://isrsvn.usurf.usu.edu/trac/isr/changeset/21296/trunk/sdlExtern/include/boost/gil/channel.hpp)
* channel_algorithm: svn [16258](https://isrsvn.usurf.usu.edu/trac/isr/changeset/16258), [17210](https://isrsvn.usurf.usu.edu/trac/isr/changeset/17210#file88)
* color_convert.hpp: svn [21296](https://isrsvn.usurf.usu.edu/trac/isr/changeset/21296/trunk/sdlExtern/include/boost/gil/color_convert.hpp)