move rep.int implementation closer to R-2.15.2
change prelude of rep to be closer to R-2.15.2
change rest of rep to be closer to R-2.15.2
coerce pairlists to vector lists in rep (as in R-2.15.0)
update to help(rep)
fix typo
changes to rep3, optimization as in R-2.15.2, fix