Still missing is automation and final decisions on mechanisms in general.

Revisioning: Include GLSL.std.450 version.  Also, the revision.h script now includes redirection to revision.h.

The new make-revision script regenerates glslang/Include/revision.h,
used as it always has been, but made with a git-tag version and the
the number of commits on master.

I have a pre-commit hook that will automatically do this on master,
likely often enough to work in practice, without needing pull requests
to include it.