Fixed the alignment of line numbers on moved rows in diffs.

A couple fixes were attempted in the past to fix alignment of line
numbers whne moved rows came into play. The reason they didn't work was
the (fairly reasonable) assumption that every moved row had the
'.moved-row' CSS class. This was only set for the rows with move flags,
though.

Since that's a pretty decent assumption to make, let's make it true.
Every moved row now has the '.moved-row' class applied.