Always add a slash after directory names in mkdir

[zauguin]

Needed to properly create texmf-var after recent LuaTeX changes.

[u-fischer]

Well I'm not sure how to test if that is needed or not but trust that you know what you are doing ;-) But if this diverges from upstream the buildinfo.txt file probably needs to be updated.

[zauguin]

Well I'm not sure how to test if that is needed or not but trust that you know what you are doing

As a bit of background: In new LuaTeX versions we are only allowed to run mkdir on (subdirs of the current dir and) paths starting with $TEXMFVAR followed by a slash. This works for creating luatex-cache inside of $TEXMFVAR, but when creating $TEXMFVAR itself it fails since $TEXMFVAR is not followed by anything then, especially not by a slash. Therefore $TEXMFVAR does not get created if it doesn't exist yet.

This is avoided with this change by just adding a slash at the end which is mostly ignored by mkdir, but makes the check happy.