Certificate process in openssl 1.0.2

[Susan Hinrichs]

Hi All,

With 1.0.2 openssl expanded their support of the certificate callback to 
handle pausing processing during the SSL handshake negotiation.  This 
replaces the functionality I added to the SNI callback in my patch for 
openssl 1.0.1.

With TS-3319, I'm updating the ATS callback logic to support the 
certificate callback if you are compiling against openssl 1.0.2.

There is a new hook constant, TS_SSL_CERT_HOOK.  If you had a SNI 
callback that was pausing the handshake to make decisions about the 
certificate, you can move it from the TS_SSL_SNI_HOOK to the 
TS_SSL_CERT_HOOK.

I'm finishing tidying up TS-3319.  It should be ready later today or 
tomorrow.

Susan