Form Validator: Validate values submitted via Web forms

This class is meant to provide server side validation of field values submitted via Web forms.

It can validate fields on following criteria:

- Required field
- Content ( email, digit, alpha, alpha-numeric )
- Own perl or posix regular expression
- Length ( min, max, equal )
- Only defined values ( for select, radio and checkbox )
- Forbidden values
- Field values dependecies
* Value can only exist with other field(s)
* Value must be equal to other field(s) ( ex. password verification )
* Value must exists OR/XOR other value(s)
- It handles fields named like an array ( ex. radiobox/checkbox )
- It can highlight the invalid fields ( with Smarty templates )
- It can return an array which information which fields were invalid ( with field name, or logical name )