Release update: preview freeze has begun

[Matt Zimmerman]

We have now entered the preview freeze, leading up to next week's 5.10
preview.  This means that changes in Ubuntu main should be limited to:

- Simple and safe changes
- High-impact bug fixes
- Changes which are explicitly approved as important for the preview
  release

Any and all exceptions require prior approval from me.  If you have a
critical issue and I'm not available, contact Colin
Watson.

-- 
 - mdz