This was surprisingly easy from a parsing standpoint and surprisingly
difficult to restructure execution to get useful parse errors.  E.g.,
with ignorebraces, current-shell constructs must be written with a
final semicolon or newline separator like { ... ;} but if anything
follows the closing brace the parse error will be reported in that
following part rather than where you want it at the point of the
missing separator.

I think (hope?) that this is the last bit of the nofork stuff, at
least until a complete rewrite of the tempfile hack, and I will commit
and push it in the next couple of days if no one finds anything broken
or objectionable.

Opinions on whether I should squash the patches and make one commit
vs. exposing the sausage-making by doing each of the seven patches
separately?  (I would list all the X-Seq numbers in the changelog
either way.)