Message3651

The problem was that PyDictionary was checking if the argument it was
passed had a 'keys' method and then calling it and iterating them. 
Hashtable has a keys method, but HashMap and the Map interface have a
'keySet' method.  If a keys method doesn't exist, PyDictionary iterates
the argument for key-value pairs.  However, iterating HashMap produces
the keys, not the key-value pairs.  Since strings in python are iterable
and support __len__, PyDictionary was complaining that it wasn't the
right length, ie a pair.

I've attached a patch to check if the object supports the keySet method,
and use that instead of the keys method.  I also added a bugtest.