Use less prittle way to get cache-verification status

And also, we no longer do old-style cache verification.

src/ZEO/tests/invalidation-age.txt

@@ -69,26 +69,17 @@ We'll open another client, and commit some transactions:
     ...     transaction.commit()
     >>> db.close()
 
-If we reopen the first client, we'll do quick verification.  We'll
-turn on logging so we can see this:
-
-    >>> import logging, sys
-    >>> old_logging_level = logging.getLogger().getEffectiveLevel()
-    >>> logging.getLogger().setLevel(logging.INFO)
-    >>> handler = logging.StreamHandler(sys.stdout)
-    >>> logging.getLogger().addHandler(handler)
+If we reopen the first client, we'll do quick verification.
 
     >>> db = ZEO.DB(addr, client='test') # doctest: +ELLIPSIS
-    ('localhost', ...
-    ('localhost', ...) Recovering 2 invalidations
-
-    >>> logging.getLogger().removeHandler(handler)
+    >>> db._storage._server.client.verify_result
+    'quick verification'
 
     >>> [v.x for v in db.open().root().values()]
     [1, 1, 0, 0, 0, 0, 0, 0, 0]
 
 Now, if we disconnect and commit more than 5 transactions, we'll see
-that verification is necessary:
+that we had to clear the cache:
 
     >>> db.close()
     >>> db = ZEO.DB(addr)
@@ -99,14 +90,9 @@ that verification is necessary:
     ...     transaction.commit()
     >>> db.close()
 
-    >>> logging.getLogger().addHandler(handler)
-    >>> db = ZEO.DB(addr, client='test') # doctest: +ELLIPSIS
-    ('localhost', ...
-    ('localhost', ...) Verifying cache
-    ('localhost', ...) endVerify finishing
-    ('localhost', ...) endVerify finished
-
-    >>> logging.getLogger().removeHandler(handler)
+    >>> db = ZEO.DB(addr, client='test')
+    >>> db._storage._server.client.verify_result
+    'cache too old, clearing'
 
     >>> [v.x for v in db.open().root().values()]
     [2, 2, 2, 2, 2, 2, 2, 2, 2]
@@ -128,16 +114,11 @@ do quick verification:
     >>> db.close()
 
 
-    >>> logging.getLogger().addHandler(handler)
     >>> db = ZEO.DB(addr, client='test') # doctest: +ELLIPSIS
-    ('localhost', ...
-    ('localhost', ...) Recovering 9 invalidations
-
-    >>> logging.getLogger().removeHandler(handler)
+    >>> db._storage._server.client.verify_result
+    'quick verification'
 
     >>> [v.x for v in db.open().root().values()]
     [3, 3, 3, 3, 3, 3, 3, 3, 3]
 
     >>> db.close()
-
-    >>> logging.getLogger().setLevel(old_logging_level)