Merge branch 'js/difftool-builtin'

A few hot-fixes to C-rewrite of "git difftool".

* js/difftool-builtin:
  t7800: simplify basic usage test
  difftool: fix bug when printing usage

t/t7800-difftool.sh

@@ -23,6 +23,18 @@ prompt_given ()
 	test "$prompt" = "Launch 'test-tool' [Y/n]? branch"
 }
 
+test_expect_success 'basic usage requires no repo' '
+	test_expect_code 129 git difftool -h >output &&
+	grep ^usage: output &&
+	# create a ceiling directory to prevent Git from finding a repo
+	mkdir -p not/repo &&
+	test_when_finished rm -r not &&
+	test_expect_code 129 \
+	env GIT_CEILING_DIRECTORIES="$(pwd)/not" \
+	git -C not/repo difftool -h >output &&
+	grep ^usage: output
+'
+
 # Create a file on master and change it on branch
 test_expect_success 'setup' '
 	echo master >file &&