Crashers of the day: Py_CLEAR must be used when there is a chance that the

Crashers of the day: Py_CLEAR must be used when there is a chance that the
function can be called recursively.
This was discussed in issue1020188.

In python codebase, all occurrences of Py_[X]DECREF(xxx->yyy) are suspect,
except when they appear in tp_new or tp_dealloc functions, or when
the member cannot be of a user-defined class.
Note that tp_init is not safe.

I do have a (crashing) example for every changed line.
Is it worth adding them to the test suite?

Example:

class SpecialStr(str):
    def __del__(self):
        s.close()

import cStringIO
s = cStringIO.StringIO(SpecialStr("text"))
s.close() # Segfault