minor code maintenance

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C3969
boolval() implemented

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C3970
SimpleXmlElement.ToBoolean() optimization
- avoids Create()
- avoids creating dummy enumerator

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C3971