This uses the gpg-interface.[ch] to allow signing the commit, i.e.

    $ git commit --gpg-sign -m foo
    You need a passphrase to unlock the secret key for
    user: "Junio C Hamano <gitster@pobox.com>"
    4096-bit RSA key, ID 96AFE6CB, created 2011-10-03 (main key ID 713660A7)

    [master 8457d13] foo
     1 files changed, 1 insertions(+), 0 deletions(-)

The lines of GPG detached signature are placed in a new multi-line header
field, instead of tucking the signature block at the end of the commit log
message text (similar to how signed tag is done), for multiple reasons:

 - The signature won't clutter output from "git log" and friends if it is
   in the extra header. If we place it at the end of the log message, we
   would need to teach "git log" and friends to strip the signature block
   with an option.

 - Teaching new versions of "git log" and "gitk" to optionally verify and
   show signatures is cleaner if we structurally know where the signature
   block is (instead of scanning in the commit log message).

 - The signature needs to be stripped upon various commit rewriting
   operations, e.g. rebase, filter-branch, etc. They all already ignore
   unknown headers, but if we place signature in the log message, all of
   these tools (and third-party tools) also need to learn how a signature
   block would look like.

 - When we added the optional encoding header, all the tools (both in tree
   and third-party) that acts on the raw commit object should have been
   fixed to ignore headers they do not understand, so it is not like that
   new header would be more likely to break than extra text in the commit.

A commit made with the above sample sequence would look like this:

    $ git cat-file commit HEAD
    tree 3cd71d90e3db4136e5260ab54599791c4f883b9d
    parent b87755351a47b09cb27d6913e6e0e17e6254a4d4
    author Junio C Hamano <gitster@pobox.com> 1317862251 -0700
    committer Junio C Hamano <gitster@pobox.com> 1317862251 -0700
    gpgsig -----BEGIN PGP SIGNATURE-----
     Version: GnuPG v1.4.10 (GNU/Linux)

     iQIcBAABAgAGBQJOjPtrAAoJELC16IaWr+bL4TMP/RSe2Y/jYnCkds9unO5JEnfG
     ...
     =dt98
     -----END PGP SIGNATURE-----

    foo

but "git log" (unless you ask for it with --pretty=raw) output is not
cluttered with the signature information.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

After running "git pull $there for-linus" to merge a signed tag, the
integrator may need to amend the resulting merge commit to fix typoes
in it. Teach --amend option to read the existing extra headers, and
carry them forward.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Now MERGE_HEAD records the tag objects without peeling, we could record
the result of manual conflict resolution via "git commit" without losing
the tag information. Introduce a new "mergetag" multi-line header field to
the commit object, and use it to store the entire contents of each signed
tag merged.

A commit header that has a multi-line payload begins with the header tag
(e.g. "mergetag" in this case), SP, the first line of payload, LF, and all
the remaining lines have a SP inserted at the beginning.

In hindsight, it would have been better to make "merge --continue" as the
way to continue from such an interrupted merge, not "commit", but this is
a backward compatibility baggage we would need to carry around for now.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

* nd/maint-autofix-tag-in-head:
  Accept tags in HEAD or MERGE_HEAD
  merge: remove global variable head[]
  merge: use return value of resolve_ref() to determine if HEAD is invalid
  merge: keep stash[] a local variable

Conflicts:
	builtin/merge.c

* cb/common-prefix-unification:
  rename pathspec_prefix() to common_prefix() and move to dir.[ch]
  consolidate pathspec_prefix and common_prefix
  remove prefix argument from pathspec_prefix

HEAD and MERGE_HEAD (among other branch tips) should never hold a
tag. That can only be caused by broken tools and is cumbersome to fix
by an end user with:

  $ git update-ref HEAD $(git rev-parse HEAD^{commit})

which may look like a magic to a new person.

Be easy, warn users (so broken tools can be fixed if they bother to
report) and move on.

Be robust, if the given SHA-1 cannot be resolved to a commit object,
die (therefore return value is always valid).

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Also make common_prefix_len() static as this refactoring makes dir.c
itself the only caller of this helper function.

Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Passing a prefix to a function that is supposed to find the prefix is
strange. And it's really only used if the pathspec is NULL. Make the
callers handle this case instead.

As we are always returning a fresh copy of a string (or NULL), change the
type of the returned value to non-const "char *".

Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

* jk/color-and-pager:
  want_color: automatically fallback to color.ui
  diff: don't load color config in plumbing
  config: refactor get_colorbool function
  color: delay auto-color decision until point of use
  git_config_colorbool: refactor stdout_is_tty handling
  diff: refactor COLOR_DIFF from a flag into an int
  setup_pager: set GIT_PAGER_IN_USE
  t7006: use test_config helpers
  test-lib: add helper functions for config
  t7006: modernize calls to unset

Conflicts:
	builtin/commit.c
	parse-options.c

* jc/maint-autofix-tag-in-head:
  commit: reduce use of redundant global variables