- Fixed a leak which would occur in the unsupported and highly

- Fixed a leak which would occur in the unsupported and highly
non-recommended use case of replacing a relationship on a fixed
mapped class many times, referring to an arbitrarily growing number of
target mappers.  A warning is emitted when the old relationship is
replaced, however if the mapping were already used for querying, the
old relationship would still be referenced within some registries.
fixes #3251