Disable complex errors by default

[marcioAlmada]

This optimization was planned much earlier, by design, but was delayed until now for debugging purposes.

Macros are extremely non deterministic and will follow the error path 99% of the times. Unless a parser stack is below a commit (which may halt the parser execution and report syntax problems), Error objects are created and discarded immediately after backtracking, causing a significant GC cost for no real reason.

It's still useful to have complex error objects when doing deterministic incremental parsing, unit testing or other situation where errors always promote to halting.