Clarified that the ``minKey()`` and ``maxKey()`` methods raise an exception
if no key exists satsifying the constraints.

Also improved the English in other interface docstrings.

Make undo{Log,Info} arguments act like Python slice indices when
both are non-negative.  The code used to do that before ZODB 3.4a9,
but changed to match ZODB's UML documentation.  Alas, some
(untested) code in Zope relied on the actual behavior (see the
collector report).  Changed code, docs, and tests to bless the
old behavior in these cases.

DemoStorage.UndoLog:  this was wrong in several ways.  I'm still
unsure about why it skips "packed" transactions.  That doesn't seem
right, but I don't have time to wonder about that now.

Windows trigger.__init__:  Simplify more.  The trigger can connect
after the other end has done  bind() and listen(); no need to wait
for an accept() too, and so no need to fiddle with blocking/
non-blocking or "expected" socket.error's either.

remove_loop_callback():  There were two definitions of this function.
Deleted one, changed the other to use enumerate().

poll():  This was trying to repair a bug in Python 2.2's asyncore.poll().
2.2 is no longer supported, so removed this poll().

_start_loop(), _stop_loop():  Removed; functionality folded into
reworked loop().

loop():  The signature of asyncore.loop() changed in 2.4, but this
still had "the old" signature.  Instead of sniffing the signature
of the Python in use, this does a saner thing:  the original
asyncore.loop is captured, and called from the body of this loop().
That way, (A) we don't care what asyncore.loop's signature is; and,
(B) we still call the original Python code, so debugging prints and
breakpoints (etc) stuffed into Python's asyncore no longer "vanish
by magic" when ZEO is used.

an OS-indepedent base class.

__repr__:  Use the postive_id function to embed the machine address.
Addresses with the high bit set trigger warnings before Python 2.4,
and come out as negative numbers in 2.4+.

Windows trigger.__init__:  Don't make 50 guesses at a port number
to use, let Windows pick an available port for us.  Also documented
the baffling single-thread socket setup dance, which took an hour to
reverse-engineer (in large part because it used a bare "except" w/ no
clue as to why).

a __del__ method (but probably did at some earlier time).

UndoSearch._readnext():  Add the transaction size to the return value.

sync() call back in to make it clearer.

and increase the sleep time per failing loop iteration.  The hope is
this will allow the test to pass on slower and/or "too busy" machines.
I can't test that, though, since I couldn't get the test to fail at
all on a Windows or a Linux box.

although ZODB doesn't.

the pickle shown is full of unprintable characters.

attribute.

The related txn_mgr spelling of various method arguments is
now deprecated, and a "transaction_manager" spelling is added.

latter to Jim's development version.  Hardest part turned out
to be teaching ZODB's setup.py how to "build" this version of
zope.testing (it has a lot of packages in a test directory,
where the latter is not itself a package).

Incidentally repaired an oversight in building zope.interface
too.

These config file keys changed:

section    key              was             is
-------    ---------------  --------------  -------------------------
zeo        address          socket-address  socket-binding-address
zeo        monitor-address  socket-address  socket-binding-address
zeoclient  server           socket-address  socket-connection-address

Use the same tag Zope trunk (2.8) is using.

A patch from Mark Hammond to repair a new Windows-specific
gimmick in ZEOServer.setup_win32_signals().