mod_h2 v0.5.4

• moving request handling and http/1 emulation into worker thread, offloading
  main
• some fixes in connection shutdown re race condition with still active workers
• removing reqtimeout filters on stream connections
• taking in latest alpn changes from httpd trunk, made separate npn patch for
  those who need to run with openssl 1.0.1
• fixed handling of transient bucket in stream output data (led to corrupted
  responses)
• reworked task join to eliminate race conditions during session shutdown
• info logging is less verbose