[Cython] Merging of the ctypes backend branch

[Romain Guillebert]

Hi everyone

I rebased the ctypes backend branch to the last cython commit, and I
wondered how the branch should be merged with the main cython
repository. I see 3 options : a) upload the branch without merging it b)
merge the branch but not run the test suite on ctypes by default or c)
merge the branch and run the test suite.

I think it's better to do c) but the test results shouldn't mix with the
results of the other backends.

What do you think ?

Romain