Added command line options

Added 4 options;
-h -- prints help message
-b -- runs in batch mode so that no human interaction is necessary.
      It assumes that the answer would be yes to any question it would
      have asked
-f -- force install even in an non-empty directory
-P -- argument is the path to a valid python executable.  The use
      if $PYTHON is preserved, but overridden by this option.
Response to the review of DM-1078

Changed force flag to a continue flag.  Changed syntax for testing
truth of flag values.  Removed the mention of the python used
if PYTHON is not specifically set.
Added a disclaimer about not editing newinstall.sh

newinstall.sh should not be edited in place.  Added words
to express this at the top of the file.