Treat an element as hidden if either offsetWidth or offsetHeight is 0. Fixes #13132, #10406.
Fix failing tests, add support for empty spans in Opera. Supplements #13132, #10406.
Ignore file inputs when serializing forms. File input serialization is handled by plugins. Fixes #13306.
Don't try and convert data for 204 No Content responses. Fixes #13292. Fixes #13261.