Add final entries to changelog for 0.20.

debian/changelog

-tails (0.20~rc1) unstable; urgency=low
+tails (0.20) unstable; urgency=low
 
   * Major new features
   - Install Linux kernel 3.10.3-1 from Debian unstable.
+  - Iceweasel 17.0.8esr + Torbrowser patches.
 
   * Bugfixes
   - Prevent Iceweasel from displaying a warning when leaving HTTPS web sites.
@@ -22,6 +23,7 @@ tails (0.20~rc1) unstable; urgency=low
     by default in Debian's Linux 3.9.6-1, it will later disabled in 3.9.7-1.
     It's unclear what will happen next, so let's explicitly enable it ourselves.
   - Do not display dialog when a message is sent in Claws Mail.
+  - Sync iceweasel preferences with the Torbrowser's.
 
   * Localization
   - Many translation updates all over the place.