tests/test-unbundlehash.t

wireproto: allow unbundle with hashed heads parameter (issue2126)

Current wire protocol of unbundle sends the list of all heads in the remote
repository to avoid race condition.  This causes "URL too long" error on HTTP
server when the repository has many heads.

This change allows clients to send SHA1 hash of sorted head hashes instead.
Also, this introduces "unbundlehash" capability to inform them that the server
accepts hashed heads parameter.

Test wire protocol unbundle with hashed heads (capability: unbundlehash)

Create a remote repository.

  $ hg init remote
  $ hg serve -R remote --config web.push_ssl=False --config web.allow_push=* -p $HGPORT -d --pid-file=hg1.pid -E error.log -A access.log
  $ cat hg1.pid >> $DAEMON_PIDS

Clone the repository and push a change.

  $ hg clone http://localhost:$HGPORT/ local
  no changes found
  updating to branch default
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ touch local/README
  $ hg ci -R local -A -m hoge
  adding README
  $ hg push -R local
  pushing to http://localhost:$HGPORT/
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files

Ensure hashed heads format is used.
The hash here is always the same since the remote repository only has the null head.

  $ cat access.log | grep unbundle
  * - - [*] "POST /?cmd=unbundle&heads=686173686564+6768033e216468247bd031a0a2d9876d79818f8f HTTP/1.1" 200 - (glob)