Use native Mac OSX Dialog to select directory for screenshot

Use native Mac OSX Dialog to select directory for screenshot
QTBUG-16722 has already been fixed (For reference: http://bugreports.qt.nokia.com/browse/QTBUG-16722)

In ConfigurationDialog.cpp, delete line435-438 and line440
I have tested it on my Mac OSX 10.9.2 and it works OK

The code:
void ConfigurationDialog::browseForScreenshotDir()
{
 QString oldScreenshorDir = StelFileMgr::getScreenshotDir();
  QString newScreenshotDir = QFileDialog::getExistingDirectory(NULL, q_("Select screenshot directory"), oldScreenshorDir, QFileDialog::ShowDirsOnly);

 if (!newScreenshotDir.isEmpty()) {
  // remove trailing slash
  if (newScreenshotDir.right(1) == "/")
   newScreenshotDir = newScreenshotDir.left(newScreenshotDir.length()-1);

  ui->screenshotDirEdit->setText(newScreenshotDir);
 }
}