LUCENE-4713: The SPI components used to load custom codecs or analysis components were fixed to also scan the Lucene ClassLoader in addition to the context ClassLoader, so Lucene is always able to find its own codecs. The special case of a null context ClassLoader is now also supported.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1455860 13f79535-47bb-0310-9956-ffa450edef68