t/test-lib-functions.sh: support `--notick` in `test_commit_bulk()`

One of the tests we'll want to add for pseudo-merge bitmaps needs to be
able to generate a large number of commits at a specific date.

Support the `--notick` option (with identical semantics to the
`--notick` option for `test_commit()`) within `test_commit_bulk` as a
prerequisite for that. Callers can then set the various _DATE variables
themselves.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib-functions.sh

@@ -458,6 +458,7 @@ test_commit_bulk () {
 	indir=.
 	ref=HEAD
 	n=1
+	notick=
 	message='commit %s'
 	filename='%s.t'
 	contents='content %s'
@@ -488,6 +489,9 @@ test_commit_bulk () {
 			filename="${1#--*=}-%s.t"
 			contents="${1#--*=} %s"
 			;;
+		--notick)
+			notick=yes
+			;;
 		-*)
 			BUG "invalid test_commit_bulk option: $1"
 			;;
@@ -507,7 +511,10 @@ test_commit_bulk () {
 
 	while test "$total" -gt 0
 	do
-		test_tick &&
+		if test -z "$notick"
+		then
+			test_tick
+		fi &&
 		echo "commit $ref"
 		printf 'author %s <%s> %s\n' \
 			"$GIT_AUTHOR_NAME" \