[v3] concept check macros, excess-errors

[Benjamin Kosnik]

> Ah, speaking of stl-inst.cc, the __sink_unused_warning<> function that's
> being conditionally specialized in that file doesn't exist.  The primary
> definition was in the old concept-checking code, now gone.  Do we still
> need those explicit instantiations?  I don't see it used anywhere else.

I guess not. If you can remove them without breaking things, then please do!

thanks,
benjamin