got registered. (Deja vu all over again. ;)

Changed to commit objects in registration order and to allow
additional objects to get registered while commiting. (The
later was wanted by PJE.)

Added a comment in commit to explain the "invariant".

Fixed bug that caused objects to get multiply aborted.  Now always
clear object registry on commit and abort. This seems like a good
idea anyway. (We were relying on free_transaction to have the
same effect. This faild miserably in single-threaded apps and
in certain error conditions.

Added a teeny optimization in get_transaction().

transparent Pythonic sematics for __setattr__ and __delattr__.
If these methods are implemented, then they *must*::

  self._p_changed=1 # prefered

or::

  self.__changed__(1) # if people get the heebe-jeebees from setting attrs

to manually register that an object's persistent state has changed, if,
in fact, it has.

Fixed "while objects" loop in commit to do the right thing with the object list element (toss it) if it doesn't have a _p_jar.  Not doing this was causing an infinite loop.

Added macro, PERSISTENCE_FLAGS, that contains the standard persistence ExtensionClass class flags. This macro is provided to make it easier to maintain persistent base classes.

with standard Python semantics.

when tpc_begin failed.

implementation a little more orthodox and, more importantly, allows
ZEO perform stores asynchronously (and then synchronize on the
vote).

Made unpickler show the data from a pickled instance when it can't load the object from the ZODB for whatever reason.  Helps when trying to debug why your object won't load.

This reduced the amount of code and should
make the next step, adding failure handling,
much easier.

Also changed invalidation protocol to be atomic
(or close enough).

skip oid DECREFing logic.

parent is killed first.  (Otherwise, sometimes - often - a new child
was being spawned before the parent was clobbered, and the zeo server
survived...)