Make sure to preserve backing votes (#6382)

* Guide updates

* Consider more dead forks.

* Ensure backing votes don't get overridden.

* Fix spelling.

* Fix comments.

* Update node/primitives/src/lib.rs

Co-authored-by: Tsvetomir Dimitrov <tsvetomir@parity.io>

Co-authored-by: eskimor <eskimor@no-such-url.com>
Co-authored-by: Tsvetomir Dimitrov <tsvetomir@parity.io>