[Pharo-project] Issue 5276: replaced MCMethodDefinition's Definitions class variable with a class instance variable.

levente did the following in squeak - replaced MCMethodDefinition's Definitions class variable with a class instance variable. The cached definitions are no longer registered for finalization. - a bit of cleanup around MCDefinition's Instances class variable And I like the idea that we do not stress the finalization. Now we should check that I understand correctly http://code.google.com/p/pharo/issues/detail?id=5276 Stef