When temporarily decoding an incoming attribute name from a unicode string, be careful not to destroy the temoporary PyObject until we're done using its char* buffer. Fixes zopefoundation/Acquisition#5.

[ci skip]

Only in ASCII encoding.

Fixes LP #143358.

Cherry-pick 8e455700 from master.

Fixes LP #1387363.

Cherry-pick cdfad147 and
ea7ef69d from master.

LP #1155760.

Cherry-pick 7b5c5fd1 from master.

Pull in a copy of ExtensionClass.h from 2.13.2 (we don't have 'svn:external'
to kick around any more).

Fixed a segfault on 64bit platforms when providing the `explicit` argument to the aq_acquire method of an Acquisition wrapper. Thx to LP #675064 for the hint to the solution. The code passed an int instead of a pointer into a function.

  ``unicode(wrapped)`` was calling ``__str__`` with an unwrapped ``self``.

(reported by David Glick on zope-dev)

Document strange behavior with parent pointer cycles involving an intermediate object, but show that these don't lead to infinite recursion