TAXIIBase: get all members properly
TAXIIBase: get all members properly

Instead of getting everything from dir() and then filtering out anything
not in __dict__, just get everything directly from vars()
(which essentially returns keys of __dict__).

Also fixed "callable(attr)" always returning False as "attr" is a string here.

TAXIIProject/libtaxii,Intelworks/libtaxii