Add extra doc line expanding on the role of the prefetch attribute
Reword the having attribute reference
Update 'as' vs '-as' discussion in ResultSet.pm

Call me pedantic, but I think moving the statment to a new line makes it
more prominant. I may have seen it before heading to irc to ask why it's
broken. Yes I should have read the section fully, but I didn't.

Also made the two statements use the same terminiolgy to be consistent
and add context.