Build Issue
There's a build issue with the latest version. The issue is that an `import time` statement in `tslib.pyx` triggers an error from Cython stating: "Assignment to non-lvalue 'time'"

`git bisect` between `HEAD` and the SHA1 of the 10.1 release (builds correctly) shows that 015447a introduces this bug. What's strange is that I've successfully compiled pandas many times since this commit.

I thought it might be a Cython issue so I tried a simple `import time` statement using IPython's cython cell magic and that works. Also, my fork with the latest changes also builds correctly. It builds correctly when `import time` is moved to the top of the file. I'm guessing that `PyDateTime_IMPORT` imports something called `time` and another import tries to write over it although I'm not sure why that would be an issue since in regular Python the old name just gets overwritten.
