Compare fields: use another field as param
Compare fields: use another field as param

A very simple improvement to enable support for comparison between fields: simply uses "_" (underscore) as prefix of POST's key in param.

Example:
I'ld like validate that the field "first" is higher or equal to field "second". The rule for field "first" will be
min_numeric,_second
Wixel/GUMP,igorclark/GUMP