p3400: replace calls to git checkout -b' by git checkout -B'

p3400 makes a copy of the current repository to test git-rebase
performance, and creates new branches in the copy with `git checkout
-b'.  If the original repository has branches with the same name as the
script is trying to create, this operation will fail.

This replaces these calls by `git checkout -B' to force the creation and
update of these branches.

Signed-off-by: Alban Gruin <[email protected]>
Acked-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: agrn

t/perf/p3400-rebase.sh

@@ -6,9 +6,9 @@ test_description='Tests rebase performance'
 test_perf_default_repo
 
 test_expect_success 'setup rebasing on top of a lot of changes' '
-	git checkout -f -b base &&
-	git checkout -b to-rebase &&
-	git checkout -b upstream &&
+	git checkout -f -B base &&
+	git checkout -B to-rebase &&
+	git checkout -B upstream &&
 	for i in $(seq 100)
 	do
 		# simulate huge diffs
@@ -35,8 +35,8 @@ test_perf 'rebase on top of a lot of unrelated changes' '
 
 test_expect_success 'setup rebasing many changes without split-index' '
 	git config core.splitIndex false &&
-	git checkout -b upstream2 to-rebase &&
-	git checkout -b to-rebase2 upstream
+	git checkout -B upstream2 to-rebase &&
+	git checkout -B to-rebase2 upstream
 '
 
 test_perf 'rebase a lot of unrelated changes without split-index' '