tweak English form validity messages:
tweak English form validity messages:

- match Google Chrome's messages where possible
- don't include the user's input value. it could be super long or otherwise mess up the displayed message.
- make more internally consistent

pablogrela/webshim,cl4rke/webshim,tomascassidy/webshim,tomascassidy/webshim,cl4rke/webshim,tomascassidy/webshim,webdev1001/webshim,aFarkas/webshim,fashionsun/webshim,aFarkas/webshim,ilovezy/webshim,aFarkas/webshim,pablogrela/webshim,fashionsun/webshim,ilovezy/webshim,webdev1001/webshim,webdev1001/webshim,ilovezy/webshim,pablogrela/webshim,cl4rke/webshim,fashionsun/webshim