Add support to JobStatusDisplay() to update the current line on the terminal,

Add support to JobStatusDisplay() to update the current line on the terminal,
which in the future can be used to erase the line and update it with new
information such as the latest load average measurement. This uses curses
to obtain the simple control codes that are needed, and has fallback codes
in case the curses module is unavailable or raises an error. When stdout
is not a tty then the line erasing behavior is automatically disabled and
display updates are simply show on a new line.

svn path=/main/trunk/; revision=11128