t7201: abstract away SHA-1-specific constants

Adjust the test so that it computes variables for object IDs instead of
using hard-coded hashes.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7201-co.sh

@@ -230,9 +230,10 @@ test_expect_success 'switch to another branch while carrying a deletion' '
 test_expect_success 'checkout to detach HEAD (with advice declined)' '
 
 	git config advice.detachedHead false &&
+	rev=$(git rev-parse --short renamer^) &&
 	git checkout -f renamer && git clean -f &&
 	git checkout renamer^ 2>messages &&
-	test_i18ngrep "HEAD is now at 7329388" messages &&
+	test_i18ngrep "HEAD is now at $rev" messages &&
 	test_line_count = 1 messages &&
 	H=$(git rev-parse --verify HEAD) &&
 	M=$(git show-ref -s --verify refs/heads/master) &&
@@ -248,9 +249,10 @@ test_expect_success 'checkout to detach HEAD (with advice declined)' '
 
 test_expect_success 'checkout to detach HEAD' '
 	git config advice.detachedHead true &&
+	rev=$(git rev-parse --short renamer^) &&
 	git checkout -f renamer && git clean -f &&
 	GIT_TEST_GETTEXT_POISON=false git checkout renamer^ 2>messages &&
-	grep "HEAD is now at 7329388" messages &&
+	grep "HEAD is now at $rev" messages &&
 	test_line_count -gt 1 messages &&
 	H=$(git rev-parse --verify HEAD) &&
 	M=$(git show-ref -s --verify refs/heads/master) &&