model: fix bug where order of classes produces buggy models

model: fix bug where order of classes produces buggy models

The problem was a caching of a non-final information.
collect_things visit the mclassdefs of the module but they may not all
be analyzed (ie. their super-types not all identified)

To solve this we build the model in one more pass:

 - a pass to assign the super-types to each mclassdef
 - a pass to build the mclassdef hierarchy

a test file is added to prevent regressions.

Reported-by: Alexis Laferrière <alexis.laf@xymus.net>
Signed-off-by: Jean Privat <jean@pryen.org>