Z3 python plugin API's decide method broken

[linusheck]

I found some issues in the Python plugin API. The decide method uses the undefined variable t_ref:

z3/src/api/python/z3/z3.py

Line 11668 in c0e748a

t = _to_expr_ref(to_Ast(t_ref), prop.ctx())

Also, registering a decide refers to the undefined property self.decide:

z3/src/api/python/z3/z3.py

Line 11787 in c0e748a

def add_decide(self, decide):

which should have been declared here:

z3/src/api/python/z3/z3.py

Line 11728 in c0e748a

self.created = None