client: really fix ZODB monkey-patch when DB lock is not acquired

Commit 5c5c7d9a was a wrong fix because RLock
does not raise 'thread.error' like Lock (when releasing an unacquired lock).

Python >= 2.5 raises a RuntimeError and older Python raise an AssertionError.

neo/client/__init__.py

@@ -57,10 +57,10 @@ if 1:
     ###
 
     try:
-        if Connection._nexedi_fix != 4:
+        if Connection._nexedi_fix != 5:
             raise Exception("A different ZODB fix is already applied")
     except AttributeError:
-        Connection._nexedi_fix = 4
+        Connection._nexedi_fix = 5
 
         # Whenever an connection is opened (and there's usually an existing one
         # in DB pool that can be reused) whereas the transaction is already
@@ -69,14 +69,12 @@ if 1:
         # For example, there's no open transaction when a ZPublisher/Publish
         # transaction begins.
 
-        import thread
-
         def open(self, *args, **kw):
             def _flush_invalidations():
                 acquire = self._db._a
                 try:
-                    self._db._r()
-                except thread.error:
+                    self._db._r()                      # this is a RLock
+                except (AssertionError, RuntimeError): # old Python uses assert
                     acquire = lambda: None
                 try:
                     del self._flush_invalidations