[BZ#759683] Ability to collapse all subfolders of a selected folder

Submitted by Mark Edgington

Description

In version 3.13.1 a new "feature" was added to meld:

In folder comparisons, the expansion state of the tree is now remembered when you collapse and re-expand a row (Kai Willadsen)

I rely on the "bad" behavior all the time, and find it much more difficult to narrow down the set of files I want to focus on with the new behavior. For example, when I have a folder containing 50 subfolders, and there are changes in all of the subfolders, but I only want to look at the changes in one of the subfolders. Previously I could collapse the parent folder, and uncollapse it to see all of the subfolders collapsed, and then only uncollapse the subfolder of interest -- now this is no longer possible, and I can't reduce the "visual noise" of undesired folders.

My request is that meld offers some means to collapse all subfolders of a selected folder.