(TeX) Exclude files generated by morewrites

To overcome the "No room for a new \write", the morewrites package (http://www.ctan.org/pkg/morewrites) uses a file with the .mw extension

In the docs of the morewritespackage, this is explicitly mentioned on page 5, `\g__morewrites_tmp_file_tl` is defined as `\jobname.mw`