* Also validate top-level version_added.
* Fix error code.
* Produce same version_added validation error in schema than in code (and stop returning it twice).
* Return correct error codes for invalid version_added for options and return values.
* Add changelog.
* Fix forgotten closing braket.
* Accept 'historical' for some top-level version_added.
(cherry picked from commit 7e2cc7db12)
