The vast majority of the time I am perfectly happy running KDevelop with Settings/Projects/Schedule all project files for parsing unticked. The files I open and the headers they include are still being parsed which means I rarely really feel I miss functionality.
There are situations though in which I'd like an entire project to be (re)parsed. This change makes that a lot easier by adding an action to the Project Manager's context menu that works on the selected project or projects.
I've done a bit of refactoring to avoid code duplication. For now I've put the action in the context menu only; I'm not convinced this will be used often enough to warrant using the approach followed with the other menu actions which are all available in different menus.