SLING-3332 - Long startup time with many sling:alias

* applied patch. The alias optimization introduced in SLING-2521 can be turned off in particular cases (e.g. huge number of alias entries)

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1565142 13f79535-47bb-0310-9956-ffa450edef68