Remove unused imports and definitions of True/False.

src/BTrees/check.py

@@ -41,12 +41,6 @@ from BTrees.IIBTree import IIBTree, IIBucket, IISet, IITreeSet
 
 TYPE_UNKNOWN, TYPE_BTREE, TYPE_BUCKET = range(3)
 
-try:
-    True
-except NameError:
-    True = 1
-    False = 0
-
 _type2kind = {IOBTree: (TYPE_BTREE, True),
               IIBTree: (TYPE_BTREE, True),
               OIBTree: (TYPE_BTREE, True),

src/ZEO/auth/auth_digest.py

@@ -34,7 +34,6 @@ user/realm/password is used as the session key.  XXX I'm not sure if
 this is a sound approach; SRP would be preferred.
 """
 
-import base64
 import os
 import random
 import sha

src/ZEO/tests/ConnectionTests.py

@@ -16,11 +16,9 @@ import os
 import sys
 import time
 import random
-import select
 import socket
 import asyncore
 import tempfile
-import thread # XXX do we really need to catch thread.error
 import threading
 import time
 

src/ZEO/zrpc/trigger.py

@@ -16,7 +16,6 @@ import asyncore
 import os
 import socket
 import thread
-import errno
 
 if os.name == 'posix':