TemporaryStorage uses

    ._index   {} oid -> serial
    ._opickle {} oid -> data

as data store for load. However for loadBefore

    ._conflict_cache  {} (oid,serial) -> (data, time)

is reused as data store.

That would be ok if that place would be treated as data store, but given
its primary purpose - as its name suggests - was originally to be a
cache to resolve conflicts, it is "logical" that entries in this cache
are garbage-collected when entry age becomes > gc threshold.

Only now there is a problem: if an object is committed once, and time
passes, corresponding entry in ._conflict_cache will be removed. And this
would manifest itself as

    - load(oid)  -> gives latest data for the object (obtained via ._index and ._opickle)

but

    - loadBefore(oid, @head)  -> gives POSKeyError

-> Fix it by always preserving latest object revision in
._conflict_cache from being removed on GC.

The fix is important for systems that use ZODB5, or ZODB4-wc2[1] because
there ZODB.Connection switched from primarily using load to exclusively
using loadBefore.

/cc @icemac @mauritsvanrees @mgedmin @d-maurer @dwt @hannosch

Fixes: https://github.com/zopefoundation/tempstorage/issues/8
[1] nexedi/ZODB@8e7eab33

By definition IStorage level methods need to be passed in storage-level
IStorageTransactionMetaData, not regular transaction.Transaction
objects:

https://github.com/zopefoundation/ZODB/blob/5.6.0-35-g1fb097b41/src/ZODB/interfaces.py#L827-L830

Passing in there regular transaction.Transaction used to work
historically, but after https://github.com/zopefoundation/ZODB/commit/2f8cc67a
it started to fail as:

    Error in test test_conflict_cache_clears_over_time (tempstorage.tests.testTemporaryStorage.TemporaryStorageTests)
    Traceback (most recent call last):
      File "/usr/lib/python2.7/unittest/case.py", line 329, in run
        testMethod()
      File "/home/kirr/src/wendelin/z/tempstorage/src/tempstorage/tests/testTemporaryStorage.py", line 195, in test_conflict_cache_clears_over_time
        self._dostore(storage, oid1, data=MinPO(5))
      File "/home/kirr/src/wendelin/z/tempstorage/src/tempstorage/tests/testTemporaryStorage.py", line 132, in _dostore
        storage.tpc_begin(t)
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/BaseStorage.py", line 193, in tpc_begin
        ext = transaction.extension_bytes
    AttributeError: 'Transaction' object has no attribute 'extension_bytes'

-> Fix it by using storage-level transactions in tests.

* Document deprecation of this package.
* Document suggested alternatives.
* Warn at runtime about the deprecation status of the package so developers using it can get a hint even when they don't read the readme of this package.

Document deprecation of this package.

Apply suggestion
Co-Authored-By: Michael Howitz <mh@gocept.com>

* fix RuntimeError in py3
* move test requirements from tox.ini to setup.py

[skip ci]

modified:   .travis.yml
modified:   CHANGES.rst
modified:   setup.py
modified:   tox.ini

modified:   .travis.yml
modified:   CHANGES.rst
modified:   setup.py
modified:   tox.ini

cf https://docs.travis-ci.com/user/languages/python/#pypy-support

This closes #9.

modified:   .travis.yml
modified:   CHANGES.rst

... by installing an updated setuptools version.

modified:   .travis.yml

This prevents a KeyError: '\x00\x00\x00\x00\x00\x00\x00\x00'

Removed doubt-inducing version pins

fixed a bug in loadBefore

I guess there were no tests of GC.

That was made effective by recent changes in ZODB that relied more on
loadBefore for MVCC.

Oddly the change makes this loadBefore match the version it was copied
from, which github says was last changed 13 years ago. (gulp, on
multiple levels).