dir_msubsup

This tests dir='rtl' on the msubsup tag

W3C sample	WIRIS
	$\begin{array}{|ccc|}\hline \text{Test}& \text{Without dir}& \text{With dir=rtl}\\ \text{msubsup}& a_b^c& a_b^c\\ \hline\end{array}$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mtable columnlines="solid" rowlines="solid" frame="solid" columnalign="center">
    <mtr>
      <mtd>
        <mtext>Test</mtext>
      </mtd>
      <mtd>
        <mtext style="width:40%">Without dir</mtext>
      </mtd>
      <mtd>
        <mtext style="width:40%">With dir=rtl</mtext>
      </mtd>
    </mtr>
    <mtr>
      <mtd>
        <mtext>msubsup</mtext>
      </mtd>
      <mtd>
        <msubsup>
          <mi>a</mi>
          <mi>b</mi>
          <mi>c</mi>
        </msubsup>
      </mtd>
      <mtd>
        <mstyle dir="rtl">
          <msubsup>
            <mi>a</mi>
            <mi>b</mi>
            <mi>c</mi>
          </msubsup>
        </mstyle>
      </mtd>
    </mtr>
  </mtable>
</math>

Author: Frédéric WANG