Test helper functions like test_must_fail may produce
messages to stderr when they see a problem. When the tests
are run with "--verbose", this ends up on the test script's
stderr, and the user can read it.

But there's a problem. Some tests record stderr as part of
the test, like:

  test_must_fail git foo 2>output &&
  test_i18ngrep expected.message output

In this case the error text goes into "output". This makes
the --verbose output less useful (it also means we might
accidentally match it in the second, though in practice we
tend to produce these messages only on error, so we'd abort
the test when the first command fails).

Let's instead send this user-facing output directly to
descriptor 4, which always points to the original stderr (or
/dev/null in non-verbose mode). And it's already forbidden
to redirect descriptor 4, since we use it for BASH_XTRACEFD,
as explained in 9be795fbce (t5615: avoid re-using descriptor
4, 2017-12-08).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Test fixes.

* sg/test-i18ngrep:
  t: make 'test_i18ngrep' more informative on failure
  t: validate 'test_i18ngrep's parameters
  t: move 'test_i18ncmp' and 'test_i18ngrep' to 'test-lib-functions.sh'
  t5536: let 'test_i18ngrep' read the file without redirection
  t5510: consolidate 'grep' and 'test_i18ngrep' patterns
  t4001: don't run 'git status' upstream of a pipe
  t6022: don't run 'git merge' upstream of a pipe
  t5812: add 'test_i18ngrep's missing filename parameter
  t5541: add 'test_i18ngrep's missing filename parameter

"git rebase" learned to take "--allow-empty-message" option.

* gs/rebase-allow-empty-message:
  rebase: add --allow-empty-message option

The log from "git daemon" can be redirected with a new option; one
relevant use case is to send the log to standard error (instead of
syslog) when running it from inetd.

* lw/daemon-log-destination:
  daemon: add --log-destination=(stderr|syslog|none)

"git format-patch" learned to give 72-cols to diffstat, which is
consistent with other line length limits the subcommand uses for
its output meant for e-mails.

* nd/format-patch-stat-width:
  format-patch: reduce patch diffstat width to 72
  format-patch: keep cover-letter diffstat wrapped in 72 columns

* tag 'v2.16.2':
  Git 2.16.2

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

Doc update.

* ab/doc-cat-file-e-still-shows-errors:
  cat-file doc: document that -e will return some output

Doc update.

* as/read-tree-prefix-doc-fix:
  doc/read-tree: remove obsolete remark