Change handling of class_init functions

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The class_init functions from pmc and dynpmc are inserted in line into the generated class+init that does internal work. This way exposes undocumented variables to the user class_init, which is confusing.

The attached patch shows the proposed change: put the code in a static function and call that function from the generated class_init.

The only problem is that dynpmc from external modules or languages can still be using the now unneeded 'pass' variable, thus that change may need a deprecation cycle.