Reduce list indentation level.

Brings them on line with paragraphs.

This change adds extra checks to line break formatting,
since they are slammed in to the blocks after parsing.
Previously line breaks where skipped based on
white-space, but since there is none before closing
list element line, line, there will be an additional br,
if the list is inside an element that can use line
breaks, like a table cell.

Due to way the br insertion works, we need to
specifically check whether there is closing list item
before the linefeed. If there is, skip it.

This also aids RedCloth definition list generation within
table cells. Those used to generate improper markup;
the last dl was always preceded by a br, because
those RedCloth lists never started from tab-level one.