[Cython] Speed up cython for enum declarations

[Stefan Behnel]

Hi,

Stefan Behnel wrote:
> David Cournapeau wrote:
>> I managed to get a quite short code snippet: it crashes on an empty
>> file :) It also crashes on a trivial file (to make sure the empty file
>> itself was not the issue)
> 
> It still doesn't crash for an empty file, but I get it to crash on this:
> 
> 	print "test"
> 
> I'll look into this.

Should be fixed now. It was the FlattenInListTransform that still wasn't as
safe as I thought.

Stefan