added insurance that parsing will stop quickly after an error. This change
did make the parser stop faster in some cases, which required some revisions
to tests. (CVS 4010)
FossilOrigin-Name: f84d9dab110c4415d9b772f8043397640162b6b2
cause the tokenizer to abort, but the parser might do several reduce
actions prior to that abort and those reduce actions sometimes need a
valid Expr. (CVS 3980)
FossilOrigin-Name: d146f01a02579339c5dc86bbe59f246bd6c05c63
