Implement LfsProtocolServlet handling the "Git LFS v1 Batch API"
protocol [1]. Add a simple file system based LFS content store and the
debug-lfs-store command to simplify testing.

Introduce a LargeFileRepository interface to enable additional storage
implementation while reusing the same protocol implementation.

At the client side we have to configure the lfs.url, specify that
we use the batch API and we don't use authentication:

  [lfs]
	  url = http://host:port/lfs
	  batch = true
  [lfs "http://host:port/lfs"]
	  access = none

the git-lfs client appends the "objects/batch" to the lfs.url.

Hard code an Authorization header in the FileLfsRepository.getAction
because then git-lfs client will skip asking for credentials. It will
just forward the Authorization header from the response to the
download/upload request.

The FileLfsServlet supports file content storage for "Large File
Storage" (LFS) server as defined by the Github LFS API [2].

- upload and download of large files is probably network bound hence use
  an asynchronous servlet for good scalability
- simple object storage in file system with 2 level fan-out
- use LockFile to protect writing large objects against multiple
  concurrent uploads of the same object
- to prevent corrupt uploads the uploaded file is rejected if its hash
  doesn't match id given in URL

The debug-lfs-store command is used to run the LfsProtocolServlet and,
optionally, the FileLfsServlet which makes it easier to setup a
local test server.

[1]
https://github.com/github/git-lfs/blob/master/docs/api/http-v1-batch.md
[2] https://github.com/github/git-lfs/tree/master/docs/api

Bug: 472961
Change-Id: I7378da5575159d2195138d799704880c5c82d5f3
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Signed-off-by: Sasa Zivkov <sasa.zivkov@sap.com>

Compile each test in its own java_test() target so they can run in
parallel, reducing total time spent testing on large machines.

$ buck test --all
[-] PROCESSING BUCK FILES...FINISHED 0.3s [100%]
[-] BUILDING...FINISHED 2.9s [100%] (351/383 JOBS, 351 UPDATED, 0.0% CACHE MISS)
[-] TESTING...FINISHED 98.1s (3360 PASS/15 SKIP/0 FAIL)

Change-Id: I8d6541268315089299f933ed23d785b1b3431133

Construct the java_application JAR wrapped with the shell script
header.  This is enough to clone a repository over HTTPs:

  $ buck build :jgit_bin
  $ buck-out/gen/jgit_bin/jgit_bin clone https://...

Change-Id: I4aceb4e77b2ec9be76a32ec93d94f2dafe9acce6

Today there are plenty of modern build tool systems available in the
wild (in no particular order):

* http://bazel.io
* https://pantsbuild.github.io
* http://shakebuild.com
* https://ninja-build.org
* https://buckbuild.com

The attributes, that all these build tools have in common, are:

* reliable
* correct
* very fast
* reproducible

It must not always be the other build tool, this project is currently
using. Or, quoting Gerrit Code Review maintainer here:

  "Friends, don't let friends use <the other build tool system>!"

This change is non-complete implementation of JGit build in Buck,
needed by Gerrit Code Review to replace its dependency with standlone
JGit cell. This is very useful when a developer is working on both
projects and is trying to integrate changes made in JGit in Gerrit.

The supported workflow is:

  $ cd jgit
  $ emacs <hack>
  $ cd ../gerrit
  $ buck build --config repositories.jgit=../jgit gerrit

With --config repositories.jgit=../jgit jgit cell is routed through
JGit development tree.

To build jgit, issue:

  $ buck build //:jgit
  [-] PROCESSING BUCK FILES...FINISHED 0,0s

Yes, you can't measure no-op build time, given that Buck daemon is
used.

Change-Id: I301a71b19fba35a5093d8cc64d4ba970c2877a44
Signed-off-by: David Ostrovsky <david@ostrovsky.org>