Exceptions get lost inside except blocks when shadowed by exceptions raised by Cython

[scoder]

This change

 http://hg.cython.org/cython-devel/rev/24bb0456d787

breaks this code:

>>> try:
...     raise ValueError
... except:
...     print(sys.exc_info()[0] is ValueError or sys.exc_info()[0])
...     a = list(py_iterator())
...     print(sys.exc_info()[0] is ValueError or sys.exc_info()[0])
...     a = list(cy_iterator())
...     print(sys.exc_info()[0] is ValueError or sys.exc_info()[0])
True
True
True

The ValueError gets lost after the list(cy_iterator()) line, which raises a StopIteration that is caught by Python's list building code. The output of this doctest is

True
True
None

which is clearly unexpected.

[scoder]

Here is a work around that moves the problem only into Py3, so that at least Py2 works as before.

 http://hg.cython.org/cython-devel/rev/a0ebfe3b1cc2

[scoder]

see also #346

[scoder]

Fix for Py3 is implemented here:

 http://hg.cython.org/cython-devel/rev/587be39d90f9