Revision 1894163

  *) mod_http2:
     - Fixed an issue since 1.15.24 that "Server" headers in proxied requests
       were overwritten instead of preserved. [PR by @daum3ns]
     - Added directove 'H2StreamTimeout' to configure a separate value for HTTP/2
       streams, overriding server's 'Timeout' configuration. [rpluem]
     - HTTP/2 connections now use pollsets to monitor the status of the
       ongoing streams and their main connection when host OS allows this.
     - Removed work-arounds for older versions of libnghttp2 and checking
       during configure that at least version 1.15.0 is present.
     - The HTTP/2 connection state handler, based on an experiment and draft
       at the IETF http working group (abandoned for some time), has been removed.
     - H2SerializeHeaders no longer has an effect. A warning is logged when it is
       set to "on". The switch enabled the internal writing of requests to be parsed
       by the internal HTTP/1.1 protocol handler and was introduced to avoid
       potential incompatibilities during the introduction of HTTP/2.
     - Removed the abort/redo of tasks when mood swings lower the active limit.