OCSP stapling failure with letsencrypt

https://lists.exim.org/lurker/message/20161027.200905.5a2fa35f.en.html
https://lists.exim.org/lurker/message/20161028.053823.015fae2d.en.html
https://bugs.exim.org/show_bug.cgi?id=1909
https://git.exim.org/exim.git/commitdiff/ee5b1e28a271faafed2e29233e7baf2f77a77f94
https://git.exim.org/exim.git/patch/ee5b1e28a271faafed2e29233e7baf2f77a77f94