Merge branch 'js/test-git-installed'

Update the "test installed Git" mode of our test suite to work better. * js/test-git-installed: tests: explicitly use `git.exe` on Windows tests: do not require Git to be built when testing an installed Git t/lib-gettext: test installed git-sh-i18n if GIT_TEST_INSTALLED is set tests: respect GIT_TEST_INSTALLED when initializing repositories tests: fix GIT_TEST_INSTALLED's PATH to include t/helper/