l3build: Rename "savetlg" as "save"


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5266 de43f980-851b-0410-b2f7-c40aca1f87e0
l3build: Rename "checklvt" to "check"

This combines the check functionality: at present the logic is still:

 - All checks run with all engines
 - Individual checks run with one engine, default pdfTeX

I'll update this later to allow an engine argument in all cases and to
run all tests for one file if "check <file>" is given with no engine.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5267 de43f980-851b-0410-b2f7-c40aca1f87e0