shortlog: support --pretty=format: option

With this patch, the user can override the default setting, to print
the commit messages using a user format instead of the onelines of the
commits.  Example:

	$ git shortlog --pretty='format:%s (%h)' <commit>..

Note that shortlog will only respect a user format setting, as the other
formats do not make much sense.

Wished for by Andrew Morton.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-shortlog.c

@@ -154,6 +154,15 @@ void shortlog_add_commit(struct shortlog *log, struct commit *commit)
 	if (!author)
 		die("Missing author: %s",
 		    sha1_to_hex(commit->object.sha1));
+	if (log->user_format) {
+		struct strbuf buf = STRBUF_INIT;
+
+		pretty_print_commit(CMIT_FMT_USERFORMAT, commit, &buf,
+			DEFAULT_ABBREV, "", "", DATE_NORMAL, 0);
+		insert_one_record(log, author, buf.buf);
+		strbuf_release(&buf);
+		return;
+	}
 	if (*buffer)
 		buffer++;
 	insert_one_record(log, author, !*buffer ? "<none>" : buffer);
@@ -271,6 +280,8 @@ int cmd_shortlog(int argc, const char **argv, const char *prefix)
 		usage_with_options(shortlog_usage, options);
 	}
 
+	log.user_format = rev.commit_format == CMIT_FMT_USERFORMAT;
+
 	/* assume HEAD if from a tty */
 	if (!nongit && !rev.pending.nr && isatty(0))
 		add_head_to_pending(&rev);

shortlog.h

@@ -11,6 +11,7 @@ struct shortlog {
 	int wrap;
 	int in1;
 	int in2;
+	int user_format;
 
 	char *common_repo_prefix;
 	int email;