Boost (1.57) GIL gives a compilation error "Non-type template argument evaluates to -1" in channel_algorithm.hpp

We are using Boost 1.57 in our project. We are now interested in using GIL to write image files.

To #include <boost/gil/gil_all.hpp> in a translation unit raises the following error with Clang [Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)].

boost/gil/channel_algorithm.hpp:54:85:
    error: non-type template argument evaluates to -1,
           which cannot be narrowed to type 'unsigned long'

• Also surprising is that by searching the web for this error, it seems that it should have been fixed some versions ago, by ticket 7970.
• Plus, the incriminated definition seems to still be present on master.

Does anyone know the status of this ?