Inconsistency in dictionary behaviour: dict(dict) not calling__setitem__

[Terry Reedy]

Final note: one of the developers ran into a similar issue with dict and 
has opened a discussion on pydev about how the C implementation might be 
changed to have derived classes act more consistently without imposing a 
time penalty on the normal use of dict.  There might possibly be a change 
by 2.6 but I am not following the details.

tjr