Remove unnecessary checks before setting `$wp_settings_*` arrays. Adds unit test for setting a nonexistent variable to a multi-dimensional `array`.

Props scribu.
Fixes #17884.


Built from https://develop.svn.wordpress.org/trunk@25240


git-svn-id: http://core.svn.wordpress.org/trunk@25210 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Introduce `description__like` arg to `get_terms()`. Make `description__like` and `name__like` perform `LIKE`s with a wildcard on both sides of passed string. Previously, strings had to match the beginning of the name, so searching for `burrito` in `This is a burrito` would fail. Adds unit tests.

Props aaroncampbell for the original patch, 5 years ago.
Fixes #8214.


Built from https://develop.svn.wordpress.org/trunk@25241


git-svn-id: http://core.svn.wordpress.org/trunk@25211 1a063a9b-81f0-0310-95a4-ce76da25c4cd