core_tag_get_tags has incorrect definition

The external_format_value class constructor takes an integer as the second param, not a string.

'descriptionformat' => new external_format_value(PARAM_INT, 'tag description format'),

This causes the webservice documentations to throw a warning because the $required property is never set.

This issue should;

1. make the webservice documentation more robust; and
2. find, seek, destroy all incorrect calls to external_format_value