Yay! Headers are no longer broken by long strings

We really shouldn't be using images that are a fixed size and can't be
stretched vertically.  If we want a gradient effect, the bottom can't
change colors right before it cuts off
Better popup thread display
[mms] Fix determination of user confirmation in certain instances.
[mms] Fix generation of Original-Message-ID header in MDN notification (Bug #13526).
Released Horde_Mime-2.4.5
Development mode for Horde_Mime-2.4.6
[mms] Filter out relative image URLs in HTML message data.