Merge branch 'ab/test-env-helper'

Remove "git env--helper" and demote it to a test-tool subcommand.

* ab/test-env-helper:
  env-helper: move this built-in to "test-tool env-helper"

t/test-lib-functions.sh

@@ -1422,7 +1422,7 @@ test_bool_env () {
 		BUG "test_bool_env requires two parameters (variable name and default value)"
 	fi
 
-	git env--helper --type=bool --default="$2" --exit-code "$1"
+	test-tool env-helper --type=bool --default="$2" --exit-code "$1"
 	ret=$?
 	case $ret in
 	0|1)	# unset or valid bool value