Added an equalto parameter for fields and checked the max number of files in upload input

in w2fields.js :
added a control for input file : when you click the input box, the
filedialog will not open if you have max files already in the box.
in w2form.js :
added the equalto option for fields : to use it just add it to a field
entry in fields list :
{ name : 'fieldname', type:'fieldtype', equalto : 'otherfieldname'}