fix NSE package check notes

[mikabr]

dplyr commands involving any NSE don't pass package check because of namespace issues. This is a known problem for which there doesn't seem to be a great solution, hadley seems to endorse "hum really loudly and hope the problem goes away". I think we can fix it by replacing every NSE call with the corresponding SE call (e.g. select(foo) -> select_("foo")), but it's annoying.