By tracking the fieldsets that have been expanded (loaded), we can make
sure the submit watchers fire appropriately, even when the fieldsets are
collapsed down again.
Apart from hopefully fixing the publishing issues for collapsed
fieldsets, this also adds a performance gain if the users expand and
collapse the same fieldsets more than once, since the fieldsets now only
load the first time they're expanded (instead of every time).
This also - at least partially - fixes the validation issue #325
introduced by #301
kjac
394572a8fc