--HG--
extra : transplant_source : %CF%81%20%8A%8D%5B%D8%84%7FE%FFu%88%C5%BF%13.%A3%DD%BE

--HG--
extra : transplant_source : z%C2k%EC%3F%0C%A4%BF%CA1cn%2BY/%3EYI%DB%1F

--HG--
extra : transplant_source : jsU4%A9%5E%24%81S%10%94%BF%FC%BD%E9-%CA%96%BF%E2

--HG--
extra : transplant_source : %15%07%06%F7Tq%91%C6%A4%FA%11%DC%27%E9%0D%D7%FA%A1gx

--HG--
extra : transplant_source : 5%FC%EB%8D%0D%CC%F1%7C%CC%909%A9%0C%1C%C2%94Nx%E0m

test: assert that isinf returns -1 for negative infinity

Fixes for buffer protocol docs

[ci skip]

Makes sure (and documents, in a sense) that isinf's declaration as returning
a bint preserves its C semantics.

This will be useful for, e.g., implementing a fake cythonize that
can leverage the deductions made by the real cythonize, but could
have other uses as well.

Their temporaries can't be references.

Docs: how to implement PEP 3118, the buffer protocol