[PATCH v6 3/3] commit::print_summary(): don't use format_commit_message()

This attempts to fix a regression in git-commit, where non-abbreviated SHA-1s were printed in the summary.

One possible fix would be to set ctx.abbrev to DEFAULT_ABBREV in the `if` block, where format_commit_message() is used.

Instead, we do away with the format_commit_message() codeblock altogether, replacing it with a re-run of log_tree_commit().

We re-run log_tree_commit() with rev.always_show_header set, to force the invocation of show_log(). The effect of this flag can be seen from this excerpt from log-tree.c:560, the only area that rev.always_show_header is checked:

	shown = log_tree_diff(opt, commit, &log);
	if (!shown && opt->loginfo && opt->always_show_header) {
		log.parent = NULL;
		show_log(opt);
		shown = 1;
	}

We also set rev.use_terminator, so that a newline is appended at the end of the log message. Note that callers in builtin/log.c that also set rev.always_show_header don't have to set rev.use_terminator, but still get a newline, because they are wrapped in a pager.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
---

This is a reworked version of the third patch of the 'tc/commit-abbrev-fix' series; there are no changes to the first and second patches.

Changes from v5:

 - don't set rev.always_show_header immediately, so that when there is
   no diff, log_tree_commit() returns false, as before the patch;

 - when log_tree_commit() returns false (ie. no diff), set
   rev.always_show_header, and re-run log_tree_commit();

 - add a missing newline to summary output by setting
   rev.use_terminator.

See the patch message for more details.

In case you're wondering where's v5, it was sent in a private review:

  http://github.com/gitster/git/commit/c69160d

 builtin/commit.c  |   10 ++++------
 t/t7502-commit.sh |    4 ++--
 2 files changed, 6 insertions(+), 8 deletions(-)