Get_terms more general sorting in taxonomy.php

[michelwp]

taxonomy is a powerful tool than can be used not only for category, post_tag or link_category. I test it to develop multilingual set (theme + plugin) and create language and dictionary taxonomies... Some small bugs was detected (#5230, #5240). To reuse standard stable scripts, it will be good if sorting can be set not only for count, name or term_id but also for slug and why not for term_group.

current code

if ( 'count' == $orderby )
		$orderby = 'tt.count';
	else if ( 'name' == $orderby )
		$orderby = 't.name';
	else
		$orderby = 't.term_id';

expected code

if ( 'count' == $orderby )
		$orderby = 'tt.count';
	else if ( 'name' == $orderby )
		$orderby = 't.name';
	else if ( 'slug' == $orderby )
		$orderby = 't.slug';
	else if ( 'term_group' == $orderby )
		$orderby = 't.term_group';
	else
		$orderby = 't.term_id';

Hope it will be useful for other developers.

(In [6284]) Add option for ordering retrieved terms by slug or term_group. Props michelwp. fixes #5245

should also apply to wp_get_object_terms()

patch attached

(In [6843]) Add more sort options to wp_get_object_terms(). Props andy. fixes #5245