[Cython] 'with gil:' statement

[mark florisson]

>>> Could someone review the patch (which is attached)? Maybe check if I
>>> haven't missed any side cases and such?
>>
>> From a first look, the test file you added seems far too short. I would
>> expect that this feature requires a lot more testing in combination with
>> declared and undeclared local variables, type inference, several exception
>> raising and catching situations (e.g. raise in one block, catch in an outer
>> block, try-finally, ...) or looping. It may also have an impact on Vitja's
>> control flow analysis branch that's worth considering.
>
> I agree. I think I'll start a branch and work on some more tests.

I also have to adjust the function teardown locking. I'll start a
branch and report back if I get positive results.