Now curl support in mupdf finally works.
MUVIEW_X11 and MUVIEW_X11_CURL are in different directories in order to avoid
conflicts.
More testing is needed (I will do in the next hours/days) but now you can try
the curl support with, e.g.:

 $ mupdf "http://www.netbsd.org/docs/pkgsrc/pkgsrc.pdf"
Delete the part about options.mk, it's now finally present and the curl
support works...
Before importing as print/mupdf more testing and maybe some cleanup is
needed.