The last tid is already set as a result of the invalidate() calls made
in _update_cache().

previous one" check fails.  Surprise!  The test was using tid < self.tid,
not <=, so it can't be the case that the test was failing because the new
tid was equal to the last one.  Changed the test to use <=.  Maybe that's
not a good change, but, if not, then the error message is wrong <wink>.

<import>

Connection initialized _map as a dict containing a single entry
mapping the connection's fileno to the connection.  That was a misuse
of the _map variable, which is also used by the asyncore.dispatcher
base class to indicate whether the dispatcher users the default
socket_map or a custom socket_map.  A recent change to asyncore caused
it to use _map in its add_channel() and del_channel() methods, which
presumes to be a bug fix (may get ported to 2.3).  That causes our
dubious use of _map to be a problem, because we also put the
Connections in the global socket_map.  The new asyncore won't remove
it from the global socket map, because it has a custom _map.

Also change a bunch of 0/1s to False/Trues.

applications to know less about how this is implemented

The comment indicated that end could be None, and I've fleshed out the
comment with more detail.

Move setLastTid() call into block where lock is held.

Remove some unnecessary pack() calls.

abnormalization.

rather than as a (probably) unprintable character.

improve the code coverage for loadBefore() in the BDBFullStorage.

extension

This eliminates a bunch of checks that weren't exercised by the test
suite.  Not sure if they were superstition or not, but I'm willing to
risk it.

with Python's newer iteration and __contains__ protocols; optional
Boolean args to exclude endpoints on range searches).