apr_pollcb

[Jim Jagielski]

As far as I can tell, there are no real consumers of apr_pollcb_*()
other than Motorz (and Simple)... Not sure, but it looks like the
pollcb stuff may be lagging, since I'm getting some weird behavior
when using that impl. So I'll likely be moving Motorz off of
pollcb and use the "traditional" impl which has been proven in
Event.