mapper compilation work ongoing, someday it'll work....moved

mapper compilation work ongoing, someday it'll work....moved
around the initialization of MapperProperty objects to be after
all mappers are created to better handle circular compilations.
do_init() method is called on all properties now which are more
aware of their "inherited" status if so.

eager loads explicitly disallowed on self-referential relationships, or
relationships to an inheriting mapper (which is also self-referential)