l3build: Update .dtx to reflect changes in targets


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5272 de43f980-851b-0410-b2f7-c40aca1f87e0
Update draft article about l3build to use save/check not savetlg/checklvt


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5273 de43f980-851b-0410-b2f7-c40aca1f87e0