The WeakKeyDictionary constructor didn't work when a dict arg was
given.  Fixed by moving a line.  Also adding a unit test.

Bugfix candidate.

referencable (weakref.ref() raises TypeError), return 0 instead of
propogating the TypeError.
This closes SF bug #478536; bugfix candidate.

It still needs to be here to preserve the API.

depending on the cycle detector code in the library implementation.
This is a *slightly* different patch than SF patch #417795, but takes
the same approach.  (This version avoids calling the __len__() method of
the dict in the remove() functions.)
This closes SF patch #417795.

This closes SF bug #458860.

for keys that are not in the dictionary.

Weak*Dictionary.update():  No longer create a temporary list to hold the
    things that will be stuffed into the underlying dictionary.  This had
    been done so that if any of the objects used as the weakly-held value
    was not weakly-referencable, no updates would take place (TypeError
    would be raised).  With this change, TypeError will still be raised
    but a partial update could occur.  This is more like other .update()
    implementations.

Thoughout, use of the name "ref" as a local variable has been removed.  The
original use of the name occurred when the function to create a weak
reference was called "new"; the overloaded use of the name could be
confusing for someone reading the code.  "ref" used as a variable name
has been replaced with "wr" (for 'weak reference').

    parameter.

Weak*Dictionary.get():  Make the second parameter optional.

WeakKeyDictionary.has_key(), .keys():  Make these actually work!

giving it a slight facelift

WeakValueDictionary.copy(),
WeakKeyDictionary.copy():  Actually return the copy!

    dead references.