Special case the type object fail

Due to differences between PyPy and CPython the type object needs to be
special cased to raise a ValueError on PyPy as well as CPython.
Skip tests for __call__ method of builtins on PyPy

Differences between PyPy and CPython means that these tests will fail on
PyPy as they wont raise exceptions. Explicitly raising exceptions on
PyPy ensures they will pass.
Enable continuous integration testing of PyPy

Test changes to make funcsigs compatible with PyPy.