The pact reached this week between the San Diego Symphony and San Diego Opera to share a common orchestra is significant for both organizations, and the deal appears to have been reached without much acrimony, an accomplishment for two groups which have not always played well together. Part of the success of the deal was getting away from traditional notions of a merger, which usually imply pending unemployment for some musicians and staffers. Instead, orchestra and opera officials are taking pains not to use the m-word, and are instead calling the pact a “contract for services.”