This used to conflict with the util crate from the standard library, which
has long since been removed.
The import in layout has not been changed because of a conflict with the
util mod there.
During debugging, I found it useful to hook all task creation in a
central location, and util::task was the perfect place for it.
r? @pcwalton (or maybe someone else, I'm kinda sending you a bunch of
reviews today because I don't know who better to give them to)