So we will find out if anything changes in the warnings and errors
that menhir produces.

bench/good: added the known bug cutdown.mly.

or the singleton set {epsilon}.

This grammar used to contain a start symbol that accepts the empty word!

files -- it was apparently dead, since all .expected files are here.

Currently equal to the performance of the table back-end.

by reading the positions from the lexbuf just in time. No speed
difference, but this should imply less frequent minor collections.

the environment record instead of updating it. This makes
the code back-end TWICE FASTER.