Tokens with keys "0" cannot be disabled in the token_insert config

This bug comes down to a few key areas. In the settings form, anything which is not checked is assigned to false and cast then saved as "0". This is fine, however when it comes to gather the available tokens the following comparison is made to determine if the token is allowed:

$allowed_options[$token] === $token

When we are building the form, the checkboxes widget is populated with settings like so:

foreach ($tokens as $token => $description) {
  $options[$token] = $category . ' : [' . $token . '] : ' . t($description['description']);
}

Here lies out bug. If the token's key is "0" which also happens to be the default option for a disabled token state, it will be considered "enabled' erroneously. The "Entity Token" module has several tokens whose keys are 0, which can clutter up the token selection form when admins with to lock it down.