tailcall now running in a simpler model, with no eval-flags and no nre-stack rewriting; yieldto also requires one fewer bounce. Mostly from mig-nre-mods
Name functions according to 'what' instead of 'how' in the [tailcall]
machinery, in view of making public some parts of it.
Test for Bug 1884496 (not buggy on trunk).
merge trunk