[Cython] any more changes for 0.21?

[Stefan Behnel]

Hi,

I think the master branch is good enough for at least a 0.21 alpha. Are
there any pending changes that should go in before it can be released? Any
pull requests that should be considered?

We should get this in, I think:

https://github.com/cython/cython/pull/284

And the gdb tests are still broken.

Robert, could you take a look through the Sage test failures? Most of them
might be issues in Sage rather than Cython, but it's better to make sure we
can either fix or safely ignore them.

Stefan