[PATCH/RFC v4 0/13] Introduce index file format version 5

Previous rounds of the series are at $gmane/202752 and $gmane/202923 and $gmane/203088.

The modification to t3700 was removed as the smudge marker is replaced with a CE_SMUDGED flag and therefore the code doesn't interfere with the test.

Changes since the last round:

 [PATCH/RFC v4 01/13] Move index v2 specific functions to their own
 [PATCH/RFC v4 02/13] read-cache.c: Re-read index if index file
    Re-read the index file if the index file has changed since
    the first time we read it.  Checking if the index file changed
    is done by using it's stat data.

 [PATCH/RFC v4 03/13] t2104: Don't fail for index versions other than
 [PATCH/RFC v4 04/13] Add documentation of the index-v5 file format
    Documentation updates as suggested by Junio.

 [PATCH/RFC v4 05/13] Make in-memory format aware of stat_crc
 [PATCH/RFC v4 06/13] Read index-v5
    Replace the pointer casts with ptr_add makro as suggested by Junio.

    Use a CE_SMUDGED flag instaed of ce_mtime as smudge marker.

    Ignore the crc sum if we don't trust_cetime, since it may give
    us wrong results.

 [PATCH/RFC v4 07/13] Read resolve-undo data
    No longer do the conversion in resolve-undo.c but in
    read-cache-v5.c.  (The same is valid for 11/13)

 [PATCH/RFC v4 08/13] Read cache-tree in index-v5
    No longer do the conversion in cache-tree.c but in
    read-cache-v5.c.  (The same is valid for 10/13)

 [PATCH/RFC v4 09/13] Write index-v5
 [PATCH/RFC v4 10/13] Write index-v5 cache-tree data
 [PATCH/RFC v4 11/13] Write resolve-undo data for index-v5
 [PATCH/RFC v4 12/13] update-index.c: rewrite index when
    Don't introduce the force-rewrite option, but always rewrite the
    index if a index-version is given.

 [PATCH/RFC v4 13/13] p0002-index.sh: add perf test for the index