HEADS UP: New release policy

After evaluating our experience with OpenLDAP 2.4 and demands* from e.g. Symas enterprise customers, we're adopting a new release policy which will be posted on -announce shortly. The main objective is to resolve the tension between wanting to release new features as soon as they're available, vs keeping stability over the long term.

*i.e., enterprises want to avoid any version updates unless they're for a specific feature they commissioned. We considered resurrecting use of the STABLE tag but that really didn't satisfy, and its use was retired for good reasons.