py3: make contrib/import-checker.py get along with itself

Indent these imports to disable the rule of "not lexically sorted."

contrib/import-checker.py

@@ -11,6 +11,7 import sys
 # Import a minimal set of stdlib modules needed for list_stdlib_modules()
 # to work when run from a virtualenv.  The modules were chosen empirically
 # so that the return value matches the return value without virtualenv.
+if True: # disable lexical sorting checks
 import BaseHTTPServer
 import zlib