Fix for defect http://code.google.com/p/owasp-esapi-php/issues/detail?id=19
Fix for defect http://code.google.com/p/owasp-esapi-php/issues/detail?id=19

Changes 
* Fixes typo
* Fixes bug with const syntax (can't have private const's)
* move to self::types (correct syntax for PHP 5 constants) rather than $this->types (incorrect)
OWASP/PHP-ESAPI,OWASP/PHP-ESAPI,OWASP/PHP-ESAPI,gpedro/PHP-ESAPI,najamelan/PHP-ESAPI,gpedro/PHP-ESAPI,gpedro/PHP-ESAPI,najamelan/PHP-ESAPI,jollysean/PHP-ESAPI,jollysean/PHP-ESAPI,najamelan/PHP-ESAPI,jollysean/PHP-ESAPI