back-bdb search result code / protocol resultcode

Related to the sizelimit settings for the internal search, bdb_do_search() seems to have inconsistencies in the implementation return code and in the protocol result code. I made a quick patch to make bdb_do_search() use separate rc and rs->sr_err. rs->sr_err will contain the protocol resultcode so that frontend functions can examine the protocol result code as well as the return code of the backend search function. Let me know if inappropriate return codes are being used in the patch (or still in the search function).