List of fixed bugs in NEWS now automatically generated

[Roland McGrath]

> The list of bugs fixed after the initial release still needs updating 
> manually, because we don't currently do point releases so there would 
> never be a point at which the release manager runs the script for the 
> branch.  (And, thus, we don't need an extra Bugzilla field to store 
> information about branches to which a fix was backported, which we would 
> need if generating that list automatically.)
> 
> For existing release branches, the list stays in the old format.  For 2.23 
> and later branches, the list of backported fixes should be in the new 
> format (via people cut-and-pasting the bug summary).

I think we want conventions whereby one can tell from bugzilla alone which
release branches have a particular bug fixed.  That seems desireable just
for people (whether maintainers or not) trying to figure things out.  A
concrete benefit would be that it becomes possible to fully automate the
process of updating NEWS on a release branch, which I think is less
error-prone than relying on manual updates.  Eventually, we could even have
a git hook that enforces that canonical NEWS updates are included in each
commit to a release branch.