fix spacing between deferred notes

Fix spacing between deferred notes. Fixes #3

Fix based on comments from gilgamec (see issue #3).
`\marginparpush` and `\marginskip` now work as expected on deferred notes.

Reproducible example showing the problem and validating the fix:

    \documentclass{memoir}
    \usepackage{lipsum}
    \usepackage{marginfix}
    \usepackage{color}
    \marginparpush = 1cm
    \begin{document}
    \marginpar{\lipsum[2]}
    \lipsum[1]
    \marginpar{\color{red}\lipsum[2]}
    \lipsum[1]
    \marginpar{\lipsum[2]}
    \lipsum[1]
    \marginpar{\color{red}\lipsum[2]}
    \lipsum[1]
    \end{document}