Reprazent/ruby-paypal — pull request #7 by aquajach (2012-12-13 04:50:32+00:00)
Title: Revise and simplify luhn_check

The implementation of luhn_check was wrong at doubling the 1st, 3rd, 5th...digit of the reversed number. While the right way is to double the 2nd, 4th, 6th...instead.

Please check http://www.brainjar.com/js/validation/default2.asp , where it verifies 4154727623381301 is an invalid number(but was valid with old logic) and 379060513751005 is a valid number(but was invalid with old logic)