Reservations validations run over incorrect sets

Currently it appears that reservations validations are being run against all **current** and maybe also all **past** reservations. This is partially absolutely unequivocally wrong.

1. returned reservations should not affect new reservations. period. (see #318)
2. current reservations may include renewed reservations, and these can invalidate new reservations, and should not. (see #569)

We *do* want *some* validations to run against current reservations, for example to determine max-number-of-items, but we certainly do not want to run them all.