Tests: Add Database Server test for UPDATE_STORED_OBJECT_IF_EQUALS.
Database Server: Use return codes in protocol instead of boolean success.
Tests: Add Database Server test for UPDATE_IF_EQUALS with invalid fields
Docs: Update db_update_if_equals to match new error codes.
DBServer: Use channel constants, do_id constants, return code cosntants.
Docs: Updated return values for ret_code
Tests: Start Database Server test for SELECT_STORED_OBJECT