title: check for equality on slices without order
body: <p>I am trying to find a solution to check for equality in 2 slices. Unfortanely, the answers I have found require values in the slice to be in the same order. For example, <a href="http://play.golang.org/p/yV0q1_u3xR" rel="noreferrer">http://play.golang.org/p/yV0q1_u3xR</a> evaluates equality to false.<br>
   I want a solution that lets <code>[]string{"a","b","c"} == []string{"b","a","c"}</code> evaluate to <code>true</code>.<br>
  <strong>MORE EXAMPLES</strong><br>
  <code>[]string{"a","a","c"} == []string{"c","a","c"}</code> >>> <code>false</code><br>
  <code>[]string{"z","z","x"} == []string{"x","z","z"}</code> >>> <code>true</code></p>