[Dovecot] Mercurial dovecot-2.0 branch change

I got tired of seeing the HEAD branch name in hg.dovecot.org (caused by the initial import from CVS), so I finally switched to "default" branch name where it doesn't show it. But apparently now everyone using dovecot-2.0 hg needs to switch to the default branch. You should see something like:

~/cvs/dovecot-2.0% hg pull -u .. not updating, since new heads added (run 'hg heads' to see heads, 'hg merge' to merge)

Now give a command:

hg up -C default

Hopefully there won't be other problems with the change.