(closes SF bug #1008998)

* Relaxed the argument restrictions for non-operator methods.  They now
  allow any iterable instead of requiring a set.  This makes the module
  a little easier to use and paves the way for an efficient C
  implementation which can take better advantage of iterable arguments
  while screening out immutables.

* Deprecated Set.update() because it now duplicates Set.union_update()

* Adapted the tests and docs to include the above changes.

* Added more test coverage including testing identities and checking
  to make sure non-restartable generators work as arguments.

Will backport to Py2.3.1 so that the interface remains consistent
across versions.  The deprecation of update() will be changed to
a FutureWarning.

* Positive wording for the description of why < and > and = can all
  be False.

* Move to a three column table format that puts long method names
  side-by-side with their operator equivalents

* Mention that KeyError can be raised by Set.pop() and Set.remove().

* Minor tweaks to the examples.

Will backport as soon as Fred rebuilds the docs so I can confirm
the tables formatted properly

Renamed hook methods to use the double underscore convention.

Note, that list.sort() is undefined for lists of sets.
Add the ... prompt to the example so it runs in doctest.

- give subsection pages nicer names
- shorten some really long table cells; table cells can't wrap in the
  typeset version of the documentation

meanings.  I did not add new, e.g., ispropersubset() methods; we're
going nuts on those, and, e.g., there was no "friendly name" for
== either.

underlying dictionaries, there were no reasonable use cases (lexicographic
sorting of a list of sets is somewhat esoteric).  Frees the operators
for other uses (such as strict subset and superset comparisons).

Updated documentation and test suite accordingly.

latter is what the code actually does.

Remove the third column in the tables since it isn't used.