Template specialization leaks into builtin types

[robertwb]

As reported on the list

cdef extern from "file":
 cdef cppclass A[T]:
   pass

cdef func1(A[double] a):
   pass

cdef public pub_func2(double a):
   pass

fails with "Function declared public or api may not have private types"

[robertwb]

Fix at  https://github.com/cython/cython/commit/c711c46a03ebbd8c83261c7ea9694920869fe5ba