Avoid using :A modifier so this works in zsh 4.2.
Fix flipped logic.

Target directories should be created when list mode IS NOT set.
Remove offensive trailing whitespace.
Use "1" instead of "yes" for no_boost_python argument.

cctbx converts it with int.
Disable build of python extensions.

They are linked to the cctbx included boost_python, but I would prefer
to link with the system BP.  Will investigate on this later.