ikiwiki's .setup file can specify wrappergroup, and ikiwiki will set the group
of the wrappers accordingly.  Having had people encounter difficulty before
when trying to do the same thing with users (for instance, making all wrappers
6755 ikiwiki:ikiwiki), I think it would help to have "wrapperuser".  This could
only actually take effect if building the wrappers as root (not really the best
plan), but ikiwiki could at least warn if wrapperuser does not match the user
the wrapper will end up with.
