Cambia solo la regexp:
gg/mm/aaaa: var re = /^\d{1,2}\/\d{1,2}\/\d{4}$/
gg-mm-aaaa: var re = /^\d{1,2}\-\d{1,2}\-\d{4}$/
gg.mm.aaaa: var re = /^\d{1,2}\.\d{1,2}\.\d{4}$/

- oppure /: var re = /^\d{1,2}[\/\-]\d{1,2}[\/\-]\d{4}$/
- o . o /: var re = /^\d{1,2}[\/\-\.]\d{1,2}[\/\-\.]\d{4}$/