In order to validate .gitmodules files, we first need to find them
in the incoming pack.

Do it in the ObjectChecker stage. Check in the tree objects if they
point to a .gitmodules file and report the tree id and the .gitmodules
blob id.

This can be used later to check if the file is in the root of the
project and if the contents are good.

While we're here, make isMacHFSGit more accurate by detecting variants
of filenames that vary in case.

[jn: tweaked NTFS and HFS+ checking; added more tests]

Change-Id: I70802e7d2c1374116149de4f89836b9498f39582
Signed-off-by: Ivan Frade <ifrade@google.com>
Signed-off-by: Jonathan Nieder <jrn@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: I1e85a951488177993521ce177fdea212615e6164
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Document explicitly that these are untranslated to (mostly) match C git.

Change-Id: I3abcffb4fd611d053bf4373e5d6a14a66f7b9b6b

Change-Id: Iead36f53d57ead0eb3edd3f9efb63b6630c9c20c
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

Change-Id: I7c545d06b1bced678c020fab9af1382bc4416b6e
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

Change-Id: I9657125765716c874bb6ecf8844c34749cb3b069
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: I8ced7098da5b345fd9af2fdfafd1ef6a44ccee0d

Change-Id: Iaca88ec28b412e6b58e7b39a0762ba54b25f9471
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

A pack bitmap index is an additional index of compressed
bitmaps of the object graph. Furthermore, a logical API of the index
functionality is included, as it is expected to be used by the
PackWriter.

Compressed bitmaps are created using the javaewah library, which is a
word-aligned compressed variant of the Java bitset class based on
run-length encoding. The library only works with positive integer
values. Thus, the maximum number of ObjectIds in a pack file that
this index can currently support is limited to Integer.MAX_VALUE.

Every ObjectId is given an integer mapping. The integer is the
position of the ObjectId in the complete ObjectId list, sorted
by offset, for the pack file. That integer is what the bitmaps
use to reference the ObjectId. Currently, the new index format can
only be used with pack files that contain a complete closure of the
object graph e.g. the result of a garbage collection.

The index file includes four bitmaps for the Git object types i.e.
commits, trees, blobs, and tags. In addition, a collection of
bitmaps keyed by an ObjectId is also included. The bitmap for each entry
in the collection represents the full closure of ObjectIds reachable
from the keyed ObjectId (including the keyed ObjectId itself). The
bitmaps are further compressed by XORing the current bitmaps against
prior bitmaps in the index, and selecting the smallest representation.
The XOR'd bitmap and offset from the current entry to the position
of the bitmap to XOR against is the actual representation of the entry
in the index file. Each entry contains one byte, which is currently
used to note whether the bitmap should be blindly reused.

Change-Id: Id328724bf6b4c8366a088233098c18643edcf40f

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>