(formerly these were silently ignored).  The only built-in methods
that take keyword arguments are __call__, __init__ and __new__.

'slotdef' structure typedef and 'struct wrapperbase'.  By adding the
wrapper docstrings to the slotdef structure, the slotdefs array can
serve as the data structure that drives add_operators(); the wrapper
descriptor contains a pointer to slotdef structure.  This replaces
lots of custom code from add_operators() by a loop over the slotdefs
array, and does away with all the tab_xxx tables.

test dramatically:

    class T(tuple): __dynamic__ = 1
    t = T(range(1000))
    for i in range(1000): tt = tuple(t)

The speedup was about 5x compared to the previous state of CVS (1.7
vs. 8.8, in arbitrary time units).  But it's still more than twice as
slow as as the same test with __dynamic__ = 0 (0.8).

I'm not sure that I really want to go through the trouble of this kind
of speedup for every slot.  Even doing it just for the most popular
slots will be a major effort (the new slot_sq_item is 40+ lines, while
the old one was one line with a powerful macro -- unfortunately the
speedup comes from expanding the macro and doing things in a way
specific to the slot signature).

An alternative that I'm currently considering is sketched in PLAN.txt:
trap setattr on type objects.  But this will require keeping track of
all derived types using weak references.

no backwards compatibility to worry about, so I just pushed the
'closure' struct member to the back -- it's never used in the current
code base (I may eliminate it, but that's more work because the getter
and setter signatures would have to change.)

As examples, I added actual docstrings to the getset attributes of a
few types: file.closed, xxsubtype.spamdict.state.

compatibility, this required all places where an array of "struct
memberlist" structures was declared that is referenced from a type's
tp_members slot to change the type of the structure to PyMemberDef;
"struct memberlist" is now only used by old code that still calls
PyMember_Get/Set.  The code in PyObject_GenericGetAttr/SetAttr now
calls the new APIs PyMember_GetOne/SetOne, which take a PyMemberDef
argument.

As examples, I added actual docstrings to the attributes of a few
types: file, complex, instance method, super, and xxsubtype.spamlist.

Also converted the symtable to new style getattr.

This implements the 'getset' class from test_binop.py.