libcurl would attempt to resume a TLS session even if the client
certificate had changed. That is unacceptable since a server by
specification is allowed to skip the client certificate check on
resume, and may instead use the old identity which was established
by the previous certificate (or no certificate).
libcurl supports by default the use of TLS session id/ticket to
resume previous TLS sessions to speed up subsequent TLS handshakes.
They are used when for any reason an existing TLS connection
couldn't be kept alive to make the next handshake faster.
This flaw is a regression and identical to CVE-2016-5419 reported
on August 3rd 2016, but affecting a different version range.