title: rstudent() returns incorrect result for an "mlm" (linear models fitted with multiple LHS)
body: <p>I know that the support for linear models with multiple LHS is limited. But when it is possible to run a function on an "mlm" object, I would expect the results to be trusty. When using <code>rstudent</code>, strange results are produced. Is this a bug or is there some other explanation? </p>
  
  <p>In the example below <code>fittedA</code> and <code>fittedB</code> are identical, but in the case of <code>rstudent</code> the 2nd column differs.</p>
  
  <pre><code>y &lt;- matrix(rnorm(20), 10, 2)
  x &lt;- 1:10
  fittedA &lt;- fitted(lm(y ~ x))
  fittedB &lt;- cbind(fitted(lm(y[, 1] ~ x)), fitted(lm(y[, 2] ~ x)))
  rstudentA &lt;- rstudent(lm(y ~ x))
  rstudentB &lt;- cbind(rstudent(lm(y[, 1] ~ x)), rstudent(lm(y[, 2] ~ x)))
  </code></pre>