message: dfa: disable if size limit is 0
  As a special case, if the user configures a DFA size limit of 0, then we
  should never try to use it. This avoids a bit of thrashing where the DFA
  tries to senselessly run before spilling over to the NFA.
diff: @@ -71,7 +71,7 @@ pub fn can_exec(insts: &Program) -> bool {
  // If i32::MAX is the largest positive delta,
  // then -i32::MAX == i32::MIN + 1 is the largest negative delta,
  // and we are OK to use 32 bits.
  - if insts.len() > ::std::i32::MAX as usize {
  + if insts.dfa_size_limit == 0 || insts.len() > ::std::i32::MAX as usize {
  return false;
  }
  for inst in insts {
  