readdir, closedir, rewinddir with parameterless overloads

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C3873
PDO improvements:
- PDO::MYSQL_ constants
- PDO::__construct overload fix
- PDOException constructor implemented to work with Phalanger
- PDO DB connection management uses PhpResource internally

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C3874
PDO methods overload fixes

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C3875
- fopen "a" mode causes a missing file to be created
- ReflectionClass::implementsInterface()
- PDO cleanup
- PDOStatement::execute() overload fix
- PDOStatement::execute() binding cleanup
- SQLitePDODriver.Quote() properly encloses value in single quotes

git-tfs-id: [http://falcon:8080/tfs/Projects]$/Phalanger/Main;C3877