[toward-py3k] remove import with_statement (part of #2711624)
They are unneeded since we dropped python 2.5 compatibility. This will help
Python 3.3 experimentation.
option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')