Correct inline docs for `is_wp_error()`
|Reported by:||johnbillion||Owned by:||SergeyBiryukov|
The inline docs for is_wp_error() states:
Does not check to see if the parent is also WP_Error, so can't inherit WP_Error and still use this function.
This is incorrect. is_wp_error() will return the expected result when passed an object of a class which extends WP_Error because it uses is_a() internally. From the `is_a()` man page:
Checks if the object is of this class or has this class as one of its parents.
Introduced in r8900.