Replacing a few uses of mpl_has_xxx by always_void and SFINAE
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx
Merge branch 'master' of https://github.com/STEllAR-GROUP/hpx
Merge branch 'master' of https://github.com/K-ballo/hpx