Supply the error message to BugWatchUpdateWarning

[Björn Tillenius]

If you look at an oops summary for checkwatches, you'll see a bunch of BugWatchUpdateWarnings. In order to see what the warnings are, you have to look at each individual oops.

We should supply the error message when raising BugWatchUpdateWarning, so that it will be displayed in the oops summary.

E.g., this is how the oops summary looks today:

  39 BugWatchUpdateWarning:
    Other: 39 Robots: 0 Local: 0
      39 None
        OOPS-829CCW1, OOPS-829CCW18, OOPS-829CCW19, OOPS-829CCW2, OOPS-829CCW20

[Gavin Panella (allenap)]

In RF 6273.