l3build: Deal in part with the "module/"bundle" issue

As "module" is used by Lua itself, there is a need to check what type
of definition is around. We are OK here as Lua 5.2 deprecates "module" in
any case, so at some stage it will be a nil anyway.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5257 de43f980-851b-0410-b2f7-c40aca1f87e0