BP Note: freeze date postponed

All- due to unforeseen issues (with other projects), I have been unable to
work on the BP doc for the last 10-days or so. This means that I have _not_
made the changes that I committed to for this (more or less final) release.

I'm back to SDW now, but we're clearly not going to be able to vote for
release on Wednesday 26th April.

During our regular Monday-morning catch-up, we BP Editors will determine
the new freeze/vote/release schedule.

Apologies for this hiccup (and thanks to everyone for their efforts during
this sprint).

Jeremy