fixes overzealous mixin of transactional resources



I've discovered that the mixins are overworking. If we have jobs A, B and C, at they, repetitively require resources X, Y and Z, the mixins will set it up like this:

A -> X
B -> X, Y
C -> X, Y, Z

when it should be:

A -> X
B -> Y
C -> Z

this happens because the mixin decorators are using the 'required_config' directly rather than calling the 'get_required_config' method. This is a relatively benign problem as jobs with extra resources just ignore them. It makes for messy ini files, though.