The patch is for the following Feature Request http://winmerge.org/rfe/2015104
I've implemented ability to add Shell Context Menu as submenu to context menu in folder comparison view. 2 new submenus appear at the bottom of the context menu: "Shell context menu for Left" and "Shell context menu for Right". If it is impossible to show context menu for currently selected group of files, appropriate submenu is not added.
There is also a checkbox in Options dialog that can enable or disable this feature (you may want to disable it because first request of shell context menu takes some time because WinMerge loads all shell extension DLLs). It is disabled by default.
The patch is against trunk HEAD (rev.6030 for the moment of submitting).