[nmh-workers] Making OpenSSL 1.0.2 minimum version

[Ken Hornstein]

Everyone,

When researching the issue Michael Richardson brought up today, it make
me realize we really should be calling SSL_set_tlsext_host_name() so we
send the TLS extension "server name indicator".  Which is easy, it's
literally one line of code.  But that makes me ask a larger question: we
have some autoconf goo to support older libraries (pre OpenSSL 1.0.2)
that didn't support the function X509_VERIFY_PARAM_set1_host(), and I
lack the energy to research if SSL_set_tlsext_host_name() exists in
pre-1.0.2 OpenSSL.  I think at this point we should consider OpenSSL
1.0.2 the minimum supported version of OpenSSL for nmh.  This would
guarantee we are doing TLS 1.2 everywhere and clean up some #ifdefs.
Objections?

--Ken