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)

boost 1.49
* [commit](https://github.com/smanders/boost-svn/commit/f72fdc3140a13ab989d954d7608626df933e672c) where we applied this to boost 1.49
* all boost 1.49 [patch commits](https://github.com/smanders/boost-svn/commits/sdl_1_49_0)