Please people, stop including internal_config.h in generic header files
Every file including src/internal_config.h (directly or indirectly)
must be rebuilt when the cmake file or config are changed. I change
these file *a lot* during my refactorings, and I get tired of
recompiling large amount of files that were not affected in any way.
This time, all of SMPI was recompiled each time. Including the **many**
collectives that we integrated a long time ago and never changed since
then. These files are not build-configured in anyway, so please don't
make me recompiling them again and again, please.