- added operator support to class-instrumented attributes. you can now

- added operator support to class-instrumented attributes. you can now
filter() (or whatever) using <classname>.<attributename>==<whatever>.
for column based properties, all column operators work (i.e. ==, <, >,
like(), in_(), etc.).  For relation() and composite column properties,
==<instance>, !=<instance>, and ==<None> are implemented so far.
[ticket:643]