TTreeMultiset constructor bug

[izgzhen]

In 7d932b6

The following lines seem wrong:

def rep_type(self, t : Type) -> Type:
    assert isinstance(t, TMinTreeMultiset) or isinstance(t, TMaxTreeMultiset), repr(t)
    return TTreeMultiset(t.elem_type)

• Reproduction case: heuristic based boolean sat solving #109 the easy synth failure. (try make select.h TIMEOUT=900 -- seems not very successful. I will try to note down the next occurrence of this).