Merge r1708107, r1709587, r1709602, r1709995, r1710231, r1710419, r1710572, r1710583...

Merge r1708107, r1709587, r1709602, r1709995, r1710231, r1710419, r1710572, r1710583, r1715023 from trunk:

mod_ssl: performing protocol switch directly after ALPN selection, mod_http2: connection hook inits network filters to force TLS handshake, reads input only if H2Direct explicitly enabled, changes H2Direct default to off even for cleartext connections

new ap_is_allowed_protocol() for testing configured protocols, added H2Upgrade on/off directive, changed H2Direct default back to on when h2c is in Protocols

moved ssl handshake trigger from mod_http2 to new process_connection hook in mod_ssl

mod_ssl: check request-server for TLS settings compatible to handshake server, allow request if equal, renegotiation checks: remember last used cipher_suite for optimizations, deny any regnegotiation in presence of master connection

announce protocol choices on first request

fixing compilation issue for older platform

disabling protocol upgrades on slave connections

first request on master connection only reports more preferred protocols in Upgrade header

mod_ssl: follow up to r1709602.
Fix "HTTP spoken on HTTPS port" broken by the SSL handshake trigger moved to
process_connection hook (r1709602) along with H2Direct speculative read.

Submitted by: icing, ylavic
Reviewed/backported by: jim

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1715255 13f79535-47bb-0310-9956-ffa450edef68