Message7234

The test was originally created for issue 4920 in CPython, where MutableSet.pop was erroneously throwing an exception. The test introduced ended up checking the return value of pop() as well, probably to be on the safe side. However, since the underlying set() that implements MutableSet returns elements in an arbitrary order[1], checking for a specific return value means the test is implementation-dependent. I've changed it to check that the returned value is any one of the values that were initially put into the set.

[1]: http://docs.python.org/library/stdtypes.html#set.pop