log -G: ignore binary files

log -G: ignore binary files

The -G<regex> option of log looks for the differences whose patch text
contains added/removed lines that match regex.

Currently -G looks also into patches of binary files (which
according to [1]) is binary as well.

This has a couple of issues:

- It makes the pickaxe search slow. In a proprietary repository of the
  author with only ~5500 commits and a total .git size of ~300MB
  searching takes ~13 seconds

    $time git log -Gwave > /dev/null

    real    0m13,241s
    user    0m12,596s
    sys     0m0,644s

  whereas when we ignore binary files with this patch it takes ~4s

    $time ~/devel/git/git log -Gwave > /dev/null

    real    0m3,713s
    user    0m3,608s
    sys     0m0,105s

  which is a speedup of more than fourfold.

- The internally used algorithm for generating patch text is based on
  xdiff and its states in [1]

  > The output format of the binary patch file is proprietary
  > (and binary) and it is basically a collection of copy and insert
  > commands [..]

  which means that the current format could change once the internal
  algorithm is changed as the format is not standardized. In addition
  the git binary patch format used for preparing patches for git apply
  is *different* from the xdiff format as can be seen by comparing

  git log -p -a

    commit 6e95bf4bafccf14650d02ab57f3affe669be10cf
    Author: A U Thor <author@example.com>
    Date:   Thu Apr 7 15:14:13 2005 -0700

        modify binary file

    diff --git a/data.bin b/data.bin
    index f414c84..edfeb6f 100644
    --- a/data.bin
    +++ b/data.bin
    @@ -1,2 +1,4 @@
     a
     a^@a
    +a
    +a^@a

  with git log --binary

    commit 6e95bf4bafccf14650d02ab57f3affe669be10cf
    Author: A U Thor <author@example.com>
    Date:   Thu Apr 7 15:14:13 2005 -0700

        modify binary file

    diff --git a/data.bin b/data.bin
    index f414c84bd3aa25fa07836bb1fb73db784635e24b..edfeb6f501[..]
    GIT binary patch
    literal 12
    QcmYe~N@Pgn0zx1O01)N^ZvX%Q

    literal 6
    NcmYe~N@Pgn0ssWg0XP5v

  which seems unexpected.

To resolve these issues this patch makes -G<regex> ignore binary files
by default. Textconv filters are supported and also -a/--text for
getting the old and broken behaviour back.

The -S<block of text> option of log looks for differences that changes
the number of occurrences of the specified block of text (i.e.
addition/deletion) in a file. As we want to keep the current behaviour,
add a test to ensure it stays that way.

[1]: http://www.xmailserver.org/xdiff.html

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>