Big internal change that should have no external effects: unify the

'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.