Adding some code for channel binding advertising.
Check whether we support the proposed channel binding type.
Run with own LuaSec.
util.sasl: New method to add channel binding handler to a SASL instance.
mod_saslauth: Set secure socket as SASL object user data for secure sessions.
util.sasl.scram: Use self.profile.cb for detection whether channel binding is supported or not.
mod_saslauth: Add channel binding handler for tls-unique channel binding.
util.sasl.scram: Validate channel binding data of client final message.
util.sasl.scram: Adding reference to RFC 5929 'Channel Bindings for TLS'.
util.sasl.scram: Remove some debugging output.
mod_saslauth: Check whether LuaSec supports getpeerfinished() binding.
util.sasl.scram: Checking the GS2 header for valid start flag.
sasl.util.scarm: Rearrage some code so it makes more sense.
Only advertise mechanisms needing channel binding if a channel binding backend is avaliable.
Backout ae48bf828f21
Merge Tobias SCRAM-PLUS work