Merge branch 'jk/http-server-protocol-versions'

Taking advantage of the CGI interface, http-backend has been
updated to enable protocol v2 automatically when the other side
asks for it.

* jk/http-server-protocol-versions:
  docs/protocol-v2: point readers transport config discussion
  docs/git: discuss server-side config for GIT_PROTOCOL
  docs/http-backend: mention v2 protocol
  http-backend: handle HTTP_GIT_PROTOCOL CGI variable
  t5551: test v2-to-v0 http protocol fallback

diff --cc Documentation/git-upload-pack.txt
Simple merge

diff --cc Documentation/technical/protocol-v2.txt
index 213538f1d0ebdc96e6b01869d7afe77bb09caeea,a703d37e08c10baddc45e0f4a691857b82c2daf2..59b86fcf97e0fe5ce34faa8cfb0f784476c5404c
--- 1/Documentation/technical/protocol-v2.txt
--- 2/Documentation/technical/protocol-v2.txt
+++ b/Documentation/technical/protocol-v2.txt
@@@ -81,9 -84,9 +84,12 @@@ A v2 server would reply
  Subsequent requests are then made directly to the service
  `$GIT_URL/git-upload-pack`. (This works the same for git-receive-pack).
  
 +Uses the `--http-backend-info-refs` option to
 +linkgit:git-upload-pack[1].
 +
+ The server may need to be configured to pass this header's contents via
+ the `GIT_PROTOCOL` variable. See the discussion in `git-http-backend.txt`.
+ 
  Capability Advertisement
  ------------------------
  

diff --cc http-backend.c
Simple merge