Update $.ajax() etc docs to not imply jqXHR.always() was in 1.5

[laughinghan]

It wasn't: http://jsbin.com/sitoqem/edit?js,console

Other Promise/Deferred methods like .done() and .fail() are already available in 1.5.x, but .always() isn't added until jQuery 1.6: https://api.jquery.com/deferred.always/

https://api.jquery.com/jquery.getJSON/#jqxhr-object
https://api.jquery.com/jquery.get/#jqxhr-object
https://api.jquery.com/jquery.post/#jqxhr-object
http://api.jquery.com/jQuery.ajax/#jqXHR

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[mgol]

Landed, thanks! And sorry for waiting so long.