Configure Maven build to capture test coverage using jacoco.

Add new org.eclipse.jgit.coverage Maven module to aggregate
jacoco test coverage results and generate test coverage HTML report at

org.eclipse.jgit.coverage/target/site/jacoco-aggregate/index.html

See https://www.eclemma.org/jacoco/trunk/doc/maven.html

Change-Id: Iaeec4033e448ebc16965c05ab54109c4155a307a
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

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>

The Large File Storage extension specified by GitHub [1] uses SHA-256 to
compute the ID of large files stored by the extension. Hence implement a
SHA-256 abstraction similar to the SHA-1 abstraction used by JGit.

[1] https://git-lfs.github.com/

Bug: 470333
Change-Id: I3a95954543c8570d73929e55f4a884b55dbf1b7a
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Note the the settings are slightly less restrictive for test bundles.
-Also cleanup a couple of malformed javadocs
-Update compiler warnings/errors to include default values from Juno
-We now flag diagnosed null dereference as error. We didn't do that
 earlier because of some false positives.

Change-Id: I58386d63164e65d3d8d1998da3390d99bdc7381a
Signed-off-by: Chris Aniszczyk <zx@twitter.com>

Introduce a http test bundle to make this functionality available for
EGit tests. A simple http server class is provided. The jetty version
was updated to a version that is also available via p2 (needed in EGit
UI tests).

Change-Id: I13bfc4c6c47e27d8f97d3e9752347d6d23e553d4
Signed-off-by: Jens Baumgart <jens.baumgart@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Per CQ 3448 this is the initial contribution of the JGit project
to eclipse.org.  It is derived from the historical JGit repository
at commit 3a2dd9921c.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>