This change teaches JGit to use a single commit-graph file to
accelerate commit graph walks. When new commits are added to the
repo, the commit-graph gets further and further behind, and then we
write the whole commit-graph file again to include new commits.

Multiple commit-graph files are not supported in the current
implementation. With this feature, git will write a commit-graph after
every git fetch command that downloads a pack-file from a remote.

JGit can read a commit-graph file from a buffered stream, which means
that we can provide this feature for both FileRepository and
DfsRepository.

Bug: 574368
Change-Id: Ib5c0d6678cb242870a0f5841bd413ad3885e95f6
Signed-off-by: kylezhao <kylezhao@tencent.com>

Pack better represents the purpose of the object and paves the way to
add a PackFile object that extends File.

Change-Id: I39b4f697902d395e9b6df5e8ce53078ce72fcea3
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>

This is the format given by the Eclipse legal doc generator [1].

[1] https://www.eclipse.org/projects/tools/documentation.php?id=technology.jgit

Bug: 548298
Change-Id: I8d8cabc998ba1b083e3f0906a8d558d391ffb6c4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: Id924f79c8b2c720297ebc49bf9c5d4ddd6d52547
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>

Add NoPackSignatureException and UnsupportedPackVersionException to
explicitly mark permanent unrecoverable problems with a pack 

Assume problem with a pack is permanent only if we are sure the
exception signals a non-transient problem we can't recover from:
- AccessDeniedException: we lack permissions
- CorruptObjectException: we detected corruption
- EOFException: file ended unexpectedly
- NoPackSignatureException: pack has no pack signature
- NoSuchFileException: file has gone missing
- PackMismatchException: pack no longer matches its index
- UnpackException: unpacking failed
- UnsupportedPackIndexVersionException: unsupported pack index version
- UnsupportedPackVersionException: unsupported pack version

Do not attempt to handle Errors since they are thrown for serious
problems applications should not try to recover from.

Change-Id: I2c416ce2b0e23255c4fb03a3f9a0ee237f7a484a
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>