changed vignette index entry

... it was wrong before; it had just been copied from a different
vignette. now it is right.
update scale-up vignette

filled in some TODOs, and also added an explanation of topcoding
and of attaching known populations to the survey data frame
small changes to helper functions

* add.kp now takes total.popn.size as an argument, in addition to
  a vector of known population totals
* topcode function now has an example to show in the help file