docs: backcompat updates notes on addBack

[Markus.Staab]

would be nice if the upgrade guide to 1.9 would suggest how to write code which works with "all"/older jquery versions (so lib/plugin authors can write code which works with 1.6+

​http://jquery.com/upgrade-guide/1.9/#addback-selector-replaces-andself-

a small code sample like

if (!jQuery.fn.addBack && jQuery.fn.andSelf) {
   jQuery.fn.addBack = jQuery.fn.andSelf;
}

[dmethvin]

#13658 is a duplicate of this ticket.

[dmethvin]

You can report docs issues or make pull requests at ​http://github.com/jquery/api.jquery.com/

[Markus.Staab]

ok will move the issue to githubs tracker.

[kswedberg]

Pretty sure this one belongs on the ​http://github.com/jquery/jquery.com/ repo (not *api.*).