Fixed some typos in some error handling code.

src/ZODB/DemoStorage.py

@@ -167,7 +167,7 @@ class DemoStorage(object):
             try:
                 return self.base.loadBlob(oid, serial)
             except AttributeError:
-                if not zope.interface.IBlobStorage.providBy(self.base):
+                if not ZODB.interfaces.IBlobStorage.providedBy(self.base):
                     raise ZODB.POSException.POSKeyError(oid, serial)
                 raise
         except AttributeError:
@@ -182,7 +182,7 @@ class DemoStorage(object):
             try:
                 return self.base.openCommittedBlobFile(oid, serial, blob)
             except AttributeError:
-                if not zope.interface.IBlobStorage.providBy(self.base):
+                if not ZODB.interfaces.IBlobStorage.providedBy(self.base):
                     raise ZODB.POSException.POSKeyError(oid, serial)
                 raise
         except AttributeError:

src/ZODB/tests/testDemoStorage.py

@@ -156,6 +156,21 @@ def testSomeDelegation():
 
     """
 
+def blob_pos_key_error_with_non_blob_base():
+    """
+    >>> storage = ZODB.DemoStorage.DemoStorage()
+    >>> storage.loadBlob(ZODB.utils.p64(1), ZODB.utils.p64(1))
+    Traceback (most recent call last):
+    ...
+    POSKeyError: 0x01
+
+    >>> storage.openCommittedBlobFile(ZODB.utils.p64(1), ZODB.utils.p64(1))
+    Traceback (most recent call last):
+    ...
+    POSKeyError: 0x01
+    
+    """
+
 
 def test_suite():
     suite = unittest.TestSuite((