Fix building python27-sys without Py_USING_UNICODE.
Fix building python27-sys without Py_USING_UNICODE.

naufraghi/rust-cpython,eneas193933/rust-cpython,dgrunwald/rust-cpython,naufraghi/rust-cpython,tempbottle/rust-cpython,fivejjs/rust-cpython,naufraghi/rust-cpython,novocaine/rust-cpython,dgrunwald/rust-cpython,ehiggs/rust-cpython