DebBugs comment import doesn't handle invalid dates correctly.

On Wed, Jan 23, 2008 at 10:38:26PM -0000, Graham Binns wrote:
> Private bug reported:
>
> The latest run of the DebBugs comment import code on staging highlighted
> the fact that some errors which should be caught by the DebBugs code and
> logged as WARNINGS (rather than allowing them to propagate up the stack
> and become ERRORs with tracebacks) weren't being. A copy of the logfile
> for the import run is attached; the break down of the errors is as
> follows:
>
> * Invalid Date None - occurs 604 times.
> * Message exceeds size limit - occurs 34 times.
> * utf8 codec can't decode... - occurs 5 times.
> * Unknown encoding... - occurs 3 times.
> * UnknownSender (bad email address: robert$@debath.co.uk) - occurs once.

Catching these errors and convert them to warnings aren't always the
right thing to do. Better to file one bug for each error. We need to
handle each error differently. These are in fact errors, and we need to
change our code to cope with it.

I've now split this bug up into four separate bugs:

 * This bug - Invalid dates aren't handled.
 * Bug #185609 - Oversized messages aren't handled.
 * Bug #185613 - Encoding errors aren't handled.
 * Bug #185620 - Invalid senders aren't handled.