hist.bootstrap <- function(x, nsim=100, breaks=25) {
  hist.actual <- hist(x, col="gray", breaks=breaks)
  for(bt in 1:100) {
    hist.bt <- hist(sample(x, replace=T), col="gray", breaks=breaks, plot=F)
    nb <- length(hist.bt$breaks)
    lines(c(rbind(hist.bt$breaks[-nb],hist.bt$breaks[-1],NA)),
          c(rbind(hist.bt$counts,hist.bt$counts,NA)), col="gray40")
  }
  lines(c(rbind(hist.actual$breaks[-nb],hist.actual$breaks[-1],NA)),
        c(rbind(hist.actual$counts,hist.actual$counts,NA)), lwd=3)
}