SSL: $ssl_curves (ticket #1088).

SSL: $ssl_curves (ticket #1088).

The variable contains a list of curves as supported by the client.
Known curves are listed by their names, unknown ones are shown
in hex, e.g., "0x001d:prime256v1:secp521r1:secp384r1".

Note that OpenSSL uses session data for SSL_get1_curves(), and
it doesn't store full list of curves supported by the client when
serializing a session.  As a result $ssl_curves is only available
for new sessions (and will be empty for reused ones).

The variable is only meaningful when using OpenSSL 1.0.2 and above.
With older versions the variable is empty.