Simplify the PinForm.clean method
Simplify the PinForm.clean method

I have a gut feeling that we could refactor some code out of this method, but for now I'll just clean it up a bit.

supervacuo/pinry,Stackato-Apps/pinry,QLGu/pinry,Stackato-Apps/pinry,wangjun/pinry,pinry/pinry,wangjun/pinry,MSylvia/pinry,pinry/pinry,supervacuo/pinry,rafirosenberg/pinry,MSylvia/pinry,lapo-luchini/pinry,MSylvia/pinry,supervacuo/pinry,rafirosenberg/pinry,Stackato-Apps/pinry,pinry/pinry,dotcom900825/xishi,QLGu/pinry,lapo-luchini/pinry,lapo-luchini/pinry,QLGu/pinry,pinry/pinry,dotcom900825/xishi,wangjun/pinry,lapo-luchini/pinry