[OSX] Reset errors to 0 if the OS tells us that (1) the chain is ok, (2) the certific...

[OSX] Reset errors to 0 if the OS tells us that (1) the chain is ok, (2) the certificate usage is for SSL server and (3) the server identity is confirmed (2+3 were part of an earlier fix). Without this reset we depended on the mono certificate store as an extra condition (which would requires mozroots to be executed and we want to avoid this 'duplicated' requirement and trust OSX). This does not affect iOS where no mono stores exists.