Hopefully resolved compatibility issues with multiple conditions in if.
Changed every instance of = for testing equality
to be ==. I also commented out the auto-selection
of a drive in the instance of 0 or 1 drives
present.
I still need to modify this to only backup files
for which the user has read permission (.Trashes
specifically is a problem).
Hopefully compatibility issues are narrowed down
and solved. I changed the du function to return
kb values (I don't need units as small as bytes
and this may not be supported on OSX). Threshold
value is adjusted accordingly.

I changed the cpArgs to use -R (more compatible).

Also, the ~/ directory will not itself be
examined, only its subdirectories and misc files.