exposed thereby. AFAICT these would not lead to any worse problems than
junk emitted on the backend's stdout, but we should have the option to
catch possible worse errors in future.
yy_fatal_error() call results in elog(ERROR) not exit(). This was
already fixed in the main lexer and plpgsql, but extend same technique
to all the other dot-l files. Also, on review of the possible calls
to yy_fatal_error(), it seems safe to use elog(ERROR) not elog(FATAL).