(both vertical 3 pane and normal 3 pane layouts) and for the results pane in
the addressbook. if we don't, it causes the splitter to jump up and down
forever on linux and (because it's so fast) pinging the CPU on windows.
r/sr=bienvenu
normal 3 pane layout. without a default, the splitter between the thread pane and the
message pane jumps when we switch folders, which looks bad and causes a repaint,
which is bad for folder loading performance. r=cavin, sr=bienvenu
huge thanks jan varga and hwaara for doing the lion's share of the work
to convert the folder pane to use the outliner.
reviewed by waterson, andreww, ben, hewitt, pinkerton, attinasi, hwaara, varga, sspitzer, bienvenu.
super reviewed by hyatt and sspitzer
for the end user: unread and total columns are back in folder pane (like 4.x)
also includes fixes for #80844#85376#89072#90075#93011#93963#95298#54171#78768#85088