“When an owner of land stands by when another person incurs expenditure or detriment and he knows that the other person believes that he is, or will be, entitled to an interest in the land, the court, with equitable jurisdiction, may require the owners to give effect to that belief by not asserting inconsistent rights or even by transfer of legal title. This equity ass sometimes been described as proprietary estoppel. It arises only if the parties have so acted that it would be unconscionable for the owner to assert the inconsistent rights and not to transfer title, as the case may be, and hence not only the circumstance of standing by on the one hand and of reliance on the other but also general considerations, such as fairness and which is relevant.”