shell: new no-interactive-login command to print a custom message

If I disable git-shell's interactive mode by removing the
~/git-shell-commands directory, attempts to ssh in to the service
produce a message intended for the administrator:

	$ ssh git@myserver
	fatal: Interactive git shell is not enabled.
	hint: ~/git-shell-commands should exist and have read and execute access.
	$

That is helpful for the new admin who is wondering "What? Why isn't
the git-shell I just set up working?", but once the site setup is
complete, it would be better to give the user a friendly hint that she
is on the right track, like GitHub does.

	Hi <username>! You've successfully authenticated, but
	GitHub does not provide shell access.

An appropriate greeting might even include more complex dynamic
information, like gitolite's list of repositories the user has access
to.  Add support for a ~/git-shell-commands/no-interactive-login
command that generates an arbitrary greeting.  When the user tries to
log in:

 * If the file ~/git-shell-commands/no-interactive-login exists,
   run no-interactive-login to let the server say what it likes,
   then hang up.

 * Otherwise, if ~/git-shell-commands/ is present, start an
   interactive read-eval-print loop.

 * Otherwise, print the usual configuration hint and hang up.

Reported-by: Ethan Reesor <firelizzard@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Improved-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'mg/qnx6' into pu

Still under discussion.
Not ready for inclusion.

* mg/qnx6:
  QNX: newer QNX 6.x.x is not so crippled
Merge branch 'jn/shell-disable-interactive' into pu

Expecting a reroll.
$gmane/216229

* jn/shell-disable-interactive:
  shell: new no-interactive-login command to print a custom message
  shell doc: emphasize purpose and security model
Merge branch 'mb/gitweb-highlight-link-target' into pu

Expecting a reroll.
$gmane/211935

* mb/gitweb-highlight-link-target:
  Highlight the link target line in Gitweb using CSS
Merge branch 'mb/remote-default-nn-origin' into pu

When the user does not specify what remote to interact with, we
often attempt to use 'origin'.  This can now be customized via a
configuration variable.

Expecting a reroll.
$gmane/210151

"The first remote becomes the default" bit is better done as a
separate step.

* mb/remote-default-nn-origin:
  Teach get_default_remote to respect remote.default.
  Test that plain "git fetch" uses remote.default when on a detached HEAD.
  Teach clone to set remote.default.
  Teach "git remote" about remote.default.
  Teach remote.c about the remote.default configuration setting.
  Rename remote.c's default_remote_name static variables.

Conflicts:
	builtin/remote.c
	t/t5505-remote.sh
Merge branch 'mg/unsigned-time-t' into pu

A few workarounds for systems with unsigned time_t.

* mg/unsigned-time-t:
  Fix time offset calculation in case of unsigned time_t
  date.c: fix unsigned time_t comparison
Merge branch 'hv/config-from-strbuf' into pu

Expecting a reroll.
$gmane/217163

* hv/config-from-strbuf:
  teach config parsing to read from strbuf
  config: make parsing stack struct independent from actual data source
  config: drop file pointer validity check in get_next_char()
  config: factor out config file stack management
Merge branch 'tr/line-log' into pu

* tr/line-log:
  log -L: :pattern:file syntax to find by funcname
  Implement line-history search (git log -L)
  Export rewrite_parents() for 'log -L'
  blame: introduce $ as "end of file" in -L syntax
  Refactor parse_loc

Conflicts:
	log-tree.c
Merge branch 'pc/subtree-add-before-fetch' into pu

Comments?

* pc/subtree-add-before-fetch:
  contrib/subtree: allow addition of remote branch with name not locally present
Merge branch 'gp/forbid-describe-all-match' into pu

"describe --match=<pattern> --all <commit>" ought to mean "use refs
that match <pattern> to describe <commit>; you do not have to limit
yourself to annotated tags."  But it doesn't.  Disable the
combination.

We may want to discard this if jc/describe topic turns out to be a
better idea.

* gp/forbid-describe-all-match:
  describe: make --all and --match=PATTERN mutually incompatible
Merge branch 'po/help-guides' into pu

Give more visibility to "concept guides" to help "git help" users.

Expecting a reroll.
$gmane/217384

* po/help-guides:
  help doc: include --guide option description
  help.c: add list_common_guides_help() function
  help.c: add --guide option
  help.c: use OPT_COUNTUP
  show 'git help <guide>' usage, with examples
Merge branch 'aw/setup-prefix-pathspec' into pu

Expecting a reroll.
$gmane/217618

* aw/setup-prefix-pathspec:
  setup.c: check that the pathspec magic ends with ")"
  setup.c: stop prefix_pathspec() from looping past the end of string
Merge branch 'pw/p4-symlinked-root' into pu

Expecting a reroll.
$gmane/217641

* pw/p4-symlinked-root:
  git p4: avoid expanding client paths in chdir
  git p4 test: should honor symlink in p4 client root
  git p4 test: make sure P4CONFIG relative path works
Merge branch 'kb/p4merge' into pu

* kb/p4merge:
  git-merge-one-file: revise merge error reporting
  mergetools/p4merge: create a base if none available
  mergetools/p4merge: swap LOCAL and REMOTE