htmlentities, html_entity_decode
- return values changed back to System.String (faster, no reason for PhpBytes since it is represented as string already internally)
- PHP 5.3, 5.4 ENT_* constants added (not supported yet)
- default value of encoding is "UTF-8"
- "str" argument can be both PhpBytes and System.String

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C4506