warn if github issues are not enabled

thanks, David Steinbrunner!
fixed repo casing
did review of Mail-Audit
did review of Mail-Audit-DKIM
did review of Mail-LocalDelivery
did review of Mail-Postfix-Attr
did review of Math-Calculator
did review of Math-VarRate
did review of MIME-BodyMunger
did review of Mixin-ExtraFields