title: get cell value based on header string and selected row
body: <p>For example, I have a PyQt QTableWidget which has 3 columns and 2 rows.
  The column headers are labeled A, B, and C.</p>
  
  <pre><code>A B C
  1 2 3
  4 5 6
  </code></pre>
  
  <p>This is the excerpt from my current source:</p>
  
  <pre><code>class myform(QtGui.QMainWindow):
  
      def __init__(self, parent=None):
  
          super(myform, self).__init__(parent)
  
          self.ui = Ui_mygui()
          self.ui.setupUi(self)
  
          self.ui.mytablewidget.cellClicked.connect(self.cell_was_clicked)
  
      @QtCore.pyqtSlot() # prevents executing following function twice
      def cell_was_clicked(self):
          row = self.ui.mytablewidget.currentItem().row()
          print "row=",row
          col = self.ui.mytablewidget.currentItem().column()
          print "col=",col
          item = self.ui.mytablewidget.horizontalHeaderItem(col).text()
          print "item=",item
  </code></pre>
  
  <p>My code works and when I select a row in my table.. I get the correct row and col numbers from the selection.  </p>
  
  <p>What is the code needed to return a cell value for the selected row given a specified header name?  If I select row 2 cell 1 ... how can I get the cell value of column C on the same row?</p>