LUCENENET-515: Bring back AttributeSource.GetAttribute(Type)
LUCENENET-515: Bring back AttributeSource.GetAttribute(Type)

git-svn-id: 579465d8e1dacce7a4aeecbe2d6cca1bad799e0c@1423359 13f79535-47bb-0310-9956-ffa450edef68

jpsullivan/lucenenet,zmaruo/lucenenet,jeme/lucenenet,zmaruo/lucenenet,NightOwl888/lucenenet,antiufo/lucenenet,jeme/lucenenet,antiufo/lucenenet,laimis/lucenenet,jeme/lucenenet,NightOwl888/lucenenet,apache/lucenenet,apache/lucenenet,sisve/lucenenet,apache/lucenenet,NightOwl888/lucenenet,mdissel/lucene.net,NightOwl888/lucenenet,jeme/lucenenet,laimis/lucenenet,apache/lucenenet,mdissel/lucene.net,jpsullivan/lucenenet,sisve/lucenenet