Several tests: cd inside subshell instead of around

Fixed all places where it was a straightforward change from cd'ing into a
directory and back via "cd .." to a cd inside a subshell.

Found these places with "git grep -w "cd \.\.".

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4041-diff-submodule-option.sh

@@ -85,10 +85,10 @@ EOF
 "
 
 commit_file sm1 &&
-cd sm1 &&
+head3=$(cd sm1 &&
 git reset --hard HEAD~2 >/dev/null &&
-head3=$(git rev-parse --verify HEAD | cut -c1-7) &&
-cd ..
+git rev-parse --verify HEAD | cut -c1-7
+)
 
 test_expect_success 'modified submodule(backward)' "
 	git diff-index -p --submodule=log HEAD >actual &&