schema 1.1 commit: when an attribute's simpleType has assertions and the type is a union of an atomic type and a list, the assertion context variable $value needs to have a relevant typed value. this commit provides few improvements related to this. there are also few minor refactorings and javadoc improvements.

git-svn-id: https://svn.apache.org/repos/asf/xerces/java/branches/xml-schema-1.1-dev@1429247 13f79535-47bb-0310-9956-ffa450edef68