Implement page-fnote-barsep to improve appearance

[KarlHegbloom]

Implement page-fnote-barsep to improve appearance.

Use 2*env->fn->sep below the footnote line because the footnotes are too close to the bar otherwise, especially when the footnote font size is the same as the body text, as is required by some court's legal brief styles. By doubling env->fn->sep, it looks good with either small or normal-size footnotes.