Make WP_Tax_Query->transform_query() public

[scribu]

Plugins/Themes that attempt to add front-end support for multi-taxonomy queries will find the WP_Tax_Query->transform_query() method quite handy.

For example, in my Query Multiple Taxonomies plugin, I need to convert to slugs, no matter what field the original tax query was using.

[nacin]

In [21863]:

Make WP_Tax_Query::transform_query() public. props scribu. fixes #21684.