Correct "clean" target for Lua build systems and generalise text file incl.

The "clean" target for a bundle needs to remove everything.

Following the pattern for other targets, the README files should be handled
using a variable and a loop (or here pair of loops).


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4771 de43f980-851b-0410-b2f7-c40aca1f87e0