[Cython] [BUG] PyFrozenset_CheckExact instead of PyFrozenSet_CheckExact

[Max Ivanov]

If you try to use frozenset inside your code, in .c file there will be
"PyFrozenset_CheckExact" but in python2.5/setobject.h
"PyFrozenSet_CheckExact" defined (notice "set" and "Set").

How could I define new macro in pyx file? I would like to workaround
this bug by defining macro "PyFrozenset_CheckExact" which points to
another macro: "PyFrozenSet_CheckExact"