Fix Sierra Trac query

[Mojca Miklavec]

Hi,

Just my two cents.

I would be in favour of changing the strings from cat names to
numbers, but of course this would only make sense if this was done
properly, automatically for all tickets. I'm sure that there's a way
to make such mass-edits, potentially while disabling email
notifications for that change if needed. (But I would not worry about
those emails.)

Ending up in inconsistent state with a weird mixture of names and
numbers would not make that much sense.

Mojca