revision 2.87 of cPickle.c

Do more robust test of whether global objects are accessible.

PyImport_ImportModule() is not guaranteed to return a module object.
When another type of object was returned, the PyModule_GetDict() call
return NULL and the subsequent GetItem() seg faulted.

Bug fix candidate.

----------

Once again, whitespace chances scuppered automatic backporting, so
I did this by hand.  Review probably wise -- but I have run make test!

Also incorporates revision 2.88 which was just removing a now unused
declaration.