Commit policy

[Tim Angus]

Just to clarify some things:

* All development should take place on the trunk. This includes bug
fixes, new features and experimental stuff.

* Release branches should not receive any commits that aren't also made
to the trunk. Normally you /shouldn't/ commit to release branches as
such commits are periodically merged from the trunk. These merges are
harder to perform if there are sporadic commits made in the interim.

* Under NO CIRCUMSTANCES ever commit to a tag. A tag is a static
snapshot which is intended to be unchanging.