format.bytes = function(x) {
  # returns byte sizes in pretty form
  # example: format.bytes(c(2,1030,2e6))
  round.to.half = function(x) round(x*2)/2
  s = as.character(x)
  names(s) = names(x)
  kilo = 2^10; mega = 2^20
  i = (x >= mega)
  s[i] = paste(round.to.half(x[i]/mega),"M",sep="")
  i = (x >= kilo) & (x < mega)
  s[i] = paste(round(x[i]/kilo),"k",sep="")
  s
}