Drop support for ZODB < 3.10

ZODB 3.10.4 was released almost 4 years ago, and contains significant
change how ghost objects coming from DB are initially setup.

bigfile/file_zodb.py

@@ -164,45 +164,17 @@ class _ZBigFile(BigFile):
 # Persistent that never goes to ghost state, if it was ever uptodate.
 # XXX move to common place?
 class LivePersistent(Persistent):
-    # NOTE in ZODB < 3.10 (exactly before commit a9cda7fb) objects coming from
-    # db are first created in seemingly uptodate state and then deactivated
-    # just to register them by the way to persistent machinery.
-    #
-    # In ZODB >= 3.10 such registration happens explicitly and no such first
-    # deactivation is done.
-    if not hasattr(PickleCache, 'new_ghost'):
-        _v_registered = False   # were we registered to Persistent machinery?
-    else:
-        _v_registered = True
-
     # don't allow us to go to ghost
     #
     # NOTE we can't use STICKY as that state is assumed as
     # short-lived-temporary by ZODB and is changed back to UPTODATE by
     # persistent code. In fact ZODB says: STICKY is UPTODATE+keep in memory.
     def _p_deactivate(self):
-        # on ZODB < 3.10 need to call Persistent._p_deactivate() the first time
-        # - it registers the object with its own machinery on first ghostify
-        # (which happens right before-on object load from DB) see comments in
-        # Per__p_deactivate() in persistent.
-        if not self._v_registered:
-            Persistent._p_deactivate(self)
-            # 1) prevents calling Persistent._p_deactivate() next time, and
-            # 2) causes Persistent to change state to UPTODATE
-            self._v_registered = True
-
         # just returning here won't allow Persistent._p_deactivate() run and
         # thus we'll stay in non-ghost state.
         return
 
 
-    # when creating initially (contrast to loading from DB), no need to go to
-    # Persistent._p_deactivate() even for the first time
-    def __init__(self):
-        Persistent.__init__(self)
-        self._v_registered = True
-
-
 
 # NOTE Can't inherit from Persistent and BigFile at the same time - both are C
 # types and their layout conflict. Persistent must be here for object to be

bigfile/tests/test_filezodb.py

@@ -95,11 +95,11 @@ def test_livepersistent():
     root = dbopen()
     db = root._p_jar.db()
 
-    # known to connection & cache & UPTODATE (ZODB < 3.10) or GHOST (ZODB >= 3.10)
+    # known to connection & cache & GHOST
     # right after first loading from DB
     lp = root['live']
     assert lp._p_jar   is not None
-    assert lp._p_state in (UPTODATE, GHOST)
+    assert lp._p_state is GHOST
     ci = cacheInfo(db)
     assert ci[kkey(LivePersistent)] == 1
 

setup.py

@@ -225,7 +225,7 @@ setup(
                    # ( NOTE: ZODB3 3.11 just pulls in latest ZODB _4_, so this way
                    #   specifying ZODB _3_ we allow external requirements to
                    #   specify either to use e.g. ZODB3.10 or ZODB4 )
-                   'ZODB3',
+                   'ZODB3 >= 3.10',
 
                    'six',       # compat py2/py3