CHG: the PHPSQLParserConstants class is now a Singleton to prevent static members.
CHG: the access to the constants has been changed a little bit (no longer static functions)
CHG: the constructor flips the constant arrays to speedup the access to the arrays

Maybe it is possible to add add/remove functions to change the constant arrays at runtime.

git-svn-id: https://php-sql-parser.googlecode.com/svn/trunk@1292 44dcfd11-89b7-3d55-2063-5c365055f77f