Extended Chosen to support tag inputting

Extended Chosen to support tag inputting. Unlike select, it works on normal text input fields, and when initialized, it accepts free-text based inputting, which is mostly useful for entering tags or similar.

Changes/Features:
   * When chosen-tag is created, a hidden multi-select field is created, which is compatible with original Chosen. The field name is same as text field name (names normally end with '[]' to allow multiple values - at least for PHP).
   * Added max_choices option to limited number of choices allowed to be selected/entered.
   * An ajax based tag suggestion was implemented (url taking from data parameter).
   * Chosen container width was changed using form_field_jq.outerWidth().
   * Regular expression in winnow_results was changed to accept partial match (aka contain)

Example:
   <input type="text" name="my-tag[]" id="my-tag" value="tag1,tag2,tag3">

   <script>
   $(function () {
      $('#my-tag').chosen();
      $('#my-tag').chosen('/tag_suggestions.php');
      $('#my-tag').chosen('/tag_suggestions.php', { max_choices: 6 });
   });
   </script>