Many small comment and code improvements.

Explicitly cast to float.  Else MSVC generated
legit warnings everywhere this macro was used,
warning about possible silent precision loss.

This adds a new IFBTree type, intended for use in indices.  Still
needs NEWS, still needs docs, and there are a pile of legitimate
compiler warnings on Windows that need fixing.

Forward port from ZODB 3.2.

Collector 1581:  fspack can blow up when .fs is corrupted

Repaired three places where fspack referenced an undefined global while
*trying* to raise CorruptedError.  Added new checkCorruptionInPack()
test to verify the correct exception gets raised.

Collector 1581:  fspack can blow up when .fs is corrupted

Repaired three places where fspack referenced an undefined global while
*trying* to raise CorruptedError.  Added new checkCorruptionInPack()
test to verify the correct exception gets raised.

type_and_adr():  Display the oid too.

Change ConflictError constructor to stop importing app objects.

When the ConflictError constructor is passed a pickle, extract
the module and class names without loading the pickle.  A ZEO
server doesn't necessarily have the implementation code for
application classes, and when that's so the attempt to raise
ConflictError was itself dying with an ImportError.

When the ConflictError constructor is passed a pickle, extract
the module and class names without loading the pickle.  A ZEO
server doesn't necessarily have the implementation code for
application classes, and when that's so the attempt to raise
ConflictError was itself dying with an ImportError.

This one doesn't exist on the 3.3 branch.

Move more get_pickle_metadata imports.

Import get_pickle_metadata from its new home.

Move get_pickle_metadata() into utils.py.

Try to make more sense of the ZODB pickle format "docs".

Try to make more sense of the ZODB pickle format "docs".

Try to get ring.h installed.

This spares clients from having to do it themselves repeatedly.
A dubious consequences is that Transaction.__init__ now requires a
WeakSet of synchronizer objects (or None -- so it's not a
catastrophic requirement, just irksome).

Weak sets have have pragmatic gotchas, explained in the comments
before the new WeakSet.as_weakref_list() method.  In essence, we
just took all the weak sets of connection objects and changed
everything so that a list of live objects is never materialized
anymore.  Also added new map()-like methods so that clients don't
usually need to be aware of the weakrefs under the covers.

This can't use self._connectionMap, because it needs to
know the version associated with each connection.

that the trunk is no longer strongly related to 3.3
development (the later takes place on the 3.3 branch).

There's no longer a hard limit on # of open connections per DB.

Introduced a sane scheme for raising deprecation warnings.
Sane ==

1. The machinery ensures that a "this will be removed in ZODB 3.6"
   blurb gets attached to all deprecation warnings.

and

2. It will dead easy to find these when it's time for 3.6.

This allows more extensive use of the _connectionMap() method.

This triggered some code changes.  When closing a connection,
the meaning of "the pool is too big" is debatable:  it may mean
that the number of all connections the pool knows about exceeds
pool_size, or it may mean that the stack of available
connections (a subset of all the connections) exceeds pool_size.

The code was changed to mean the latter, primarily because it's
predictable.  The total number of connections the pool knows
about can change at any time, because it depends on which weak
references DB holds that cyclic gc hasn't yet cleared.

But it doesn't matter much either way, since clients are never
"supposed to" exceed pool_size anyway.  I think it degrades
more gracefully this way.

Also test that DB's internal weakrefs don't keep a
Connection alive on their own.

This can happen during DB construction, or after the fact.