A bugtask change followed by a bug change is rendered confusingly in bug comments

[Gavin Panella]

For example:

    Changed in firefox:
       status: Triaged --> In Progress
      affects: oem-codes --> inkscape

Huh? The affects line is not related to the "Changed in firefox:"
heading, and refers to one of the bug's other bugtasks.

Previously it has been the case that we always put the bug changes
first:

      affects: oem-codes --> inkscape
    Changed in firefox:
       status: Triaged --> In Progress

That's a bit better.

However, activity that happens at approximately the same time can now
be grouped. Previously only activity that happened at *exactly* the
same time would be grouped (i.e. in the same transaction).

To avoid confusion it is important to show activity in the order it
happened, even when grouped.

We need a way to display grouped activity more clearly.

One way would be to render the "Changed in <target>:" blocks in a
different background colour, or to alternate background colours
between blocks of activity:

    | Changed in firefox: | <-- White
    | status: Triaged --> In Progress | <-- White
    | affects: oem-codes --> inkscape | <-- Light grey

There are probably better ways of doing thing though.