• mod_proxy_http2: fix retry handling to not leak temporary errors.
  On detecting that that an existing connection was shutdown by the other
  side, a 503 response leaked even though the request was retried on a
  fresh connection.
• Fixed a bug that applied request filters twice on redirects. This led to
  double chunked-encoding internally on POST requests without content-length.
  Fix by Yann Ylavic.
  See https://bz.apache.org/bugzilla/show_bug.cgi?id=66597.
• mod_proxy_http2: added checks for space/ctrls in nocanon path/urls
  before forwarding. By Yann Ylavic.