Update the access/modification times of the existing file, if there is one, in FileUtils::touch()
Update the access/modification times of the existing file, if there is one, in FileUtils::touch()

This changes FileUtils::touch() to match the documentation for the 'touch' tool
on Unix.

zhengw1985/Update-Installer,zhengw1985/Update-Installer,zhengw1985/Update-Installer