[FIX] "prefetching" removing even the records specifically asked for

16d6744 turns out to not be great, because it filters out the todos for
prefetched fields (rather than those just for the field being asked) there are
situations where it ends up not fetching the records it was originally asked
for and breaks a bunch of stuff e.g. unreconcile line in bank statements

Force the ids explicitly asked for back in the fetched set, so that the
prefetch is at most a noop, rco will have to take an actual look at it.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64