Add persistent-https to contrib

Git over HTTPS has a high request startup latency, since the SSL
negotiation can take up to a second. In order to reduce this latency,
connections should be left open to the Git server across requests
(or invocations of the git commandline).

Reduce SSL startup latency by running a daemon job that keeps
connections open to a Git server. The daemon job
(git-remote-persistent-https--proxy) is started on the first request
through the client binary (git-remote-persistent-https) and remains
running for 24 hours after the last request, or until a new daemon
binary is placed in the PATH. The client determines the daemon's
HTTP address by communicating over a UNIX socket with the daemon.
From there, the rest of the Git protocol work is delegated to the
"git-remote-http" binary, with the environment's http_proxy set to
the daemon.

Accessing /pub/scm/linux/kernel/git/torvalds/linux repository hosted
at kernel.googlesource.com with "git ls-remote" over https:// and
persistent-https:// 5 times shows that the first request takes about
the same time (0.193s vs 0.208s---there is a slight set-up cost for
the local proxy); as expected, the other four requests are much
faster (~0.18s vs ~0.08s).

Incidentally, this also has the benefit of HTTP keep-alive working
across Git command invocations. Its common for servers to use a 5
minute keep-alive on an HTTP 1.1 connection. Git-over-HTTP commonly
uses Transfer-Encoding: chunked on replies, so keep-alive will
generally just work, even though a pack stream's length isn't known
in advance. Because the helper is an external process holding that
connection open, we also benefit from being able to reuse an
existing TCP connection to the server.  The same "git ls-remote"
test against http:// vs persistent-https:// URL shows that the
former takes ~0.09s while the first request for the latter is about
0.134s with set-up cost, and subsequent requests are ~0.065s,
shaving around one RTT to the server.

Signed-off-by: Colby Ranger <cranger@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
git-svn: platform auth providers are working only on 1.6.15 or newer

Matthijs Kooijman reports that the cut-off point 082afee (git-svn:
use platform specific auth providers, 2012-04-26) set at 1.6.12 to
use this feature safely was incorrect, and it is 1.6.15 instead:

    http://svn.apache.org/repos/asf/subversion/trunk/CHANGES
    Version 1.6.15
       * improve some swig parameter mapping (r984565, r1035745)

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Acked-by: Eric Wong <normalperson@yhbt.net>
doc: fix xref link from api docs to manual pages

They are one-level above, so refer them as linkgit:../git-foo[n] with "../"

Signed-off-by: Junio C Hamano <gitster@pobox.com>
api-credentials.txt: show the big picture first

The API documentation targets two kinds of developers: those using the
C API, and those writing remote-helpers. The document was not clear
about which part was useful to which category, and for example, the C API
could be mistakenly thought as an API for writting remote helpers.

Based-on-patch-by: Jeff King <peff@peff.net>
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
api-credentials.txt: mention credential.helper explicitly

The name of the configuration variable was mentioned only at the very
end of the explanation, in a place specific to a specific rule, hence it
was not very clear what the specification was about.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
api-credentials.txt: add "see also" section

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
t3510 (cherry-pick-sequence): add missing '&&'

Breaks in a test assertion's && chain can potentially hide failures
from earlier commands in the chain.  Fix an instance of this in the
setup.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'cr/persistent-https'

A remote helper that acts as a proxy and caches ssl session for the
https:// transport is added to the contrib/ area.

By Colby Ranger
* cr/persistent-https:
  Add persistent-https to contrib
Merge branch 'jc/svn-auth-providers-unusable-at-1.6.12'

Regression fix for people with libsvn between 1.6.12 and 1.6.15, on
which we tried to use the non-working platform auth providers.

* jc/svn-auth-providers-unusable-at-1.6.12:
  git-svn: platform auth providers are working only on 1.6.15 or newer
Merge branch 'rr/maint-t3510-cascade-fix'

* rr/maint-t3510-cascade-fix:
  t3510 (cherry-pick-sequence): add missing '&&'
Merge branch 'mm/api-credentials-doc'

* mm/api-credentials-doc:
  api-credentials.txt: add "see also" section
  api-credentials.txt: mention credential.helper explicitly
  api-credentials.txt: show the big picture first
  doc: fix xref link from api docs to manual pages
Git 1.7.11-rc2

Signed-off-by: Junio C Hamano <gitster@pobox.com>