In `wp_get_object_terms()`, before returning terms (and before running them through the 'wp_get_object_terms' filter) - run them through `$terms = array_values( array_unique( $terms, SORT_REGULAR ) )`. 

There will be "dupes" when the function is called with `'fields' => 'all_with_object_id'`, but the objects will actually be unique due to the `object_id` addition, so they shouldn't be filtered out. 

Adds unit tests. All other unit tests pass.

Fixes #11003.

Built from https://develop.svn.wordpress.org/trunk@28583


git-svn-id: http://core.svn.wordpress.org/trunk@28408 1a063a9b-81f0-0310-95a4-ce76da25c4cd