obe
The ``versions`` option now defaults to ``versions`` (if there is a
``versions`` section), so you know longer need to include::

   versions = versions

in a ``buildout`` section when pinning versions.
Fixed: spaces in version constriants (e.g. ``< 2``) weren't handled
       correctly.
Added back IncompatibleVersionError as an alias for
IncompatibleConstraintError.