The registry always comes first and the default is always appended.

1. Only DECREF the class's module when the module is retrieved via
PyImport_Import.  If it is retrieved from the modules dictionary with
PyDict_GetItem, it is using a borrowed reference.

2. If the module doesn't define the desired class, raise the same
SystemError that pickle.py does instead of returning an AttributeError
(which is cryptic at best).

Also, fix the PyArg_ParseTuple in cpm_loads (the externally visible
loads) function:  Use "S" instead of "O" because cStringIO will croak
with a "bad arguments to internal function" if passed anything other
than a string.

The rest of these are new or replaced.  The buttons are now all the same
width.  They have the transparency set right.  They still need the attention
of a designer.  But they work, and we have a real button for the Modules
Index.

special "html" package, which we don't and won't.

additional processes for each name change!

displays funny characters, like spaces or control characters, more
clearly (one of my pet peeves in error messages).  Also only suppress
the filename if it is None; display it if it is '', since that would
be a genuine (illegal) filename passed in!

Small markup nits.

frozen packages.  (I *think* this means that we can now have a
built-in module bar that's a submodule of a frozen package foo, by
registering the built-in module with a name "foo.bar" in the table of
builtin modules.)