Merge: Faster lookup

Merge: Faster lookup

This series improves the lookup strategies:

* special fast track for the virtual type SELF
* choose to iterate on the mclassdefs instead of the mpropdefs if they are less numerous.

This mainly limit the degenerative cases that where discovered while investigating the slowdown of #2223

with nitc/nitc/nitc:
before: 0m7.168s
after: 0m6.232s

with nitpick ../contrib:
before: 0m20.928s
after: 0m19.432s

Pull-Request: #2245
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>