title: stat_summary2d missing an already supplied aesthetic?
body: <p>This code works as it should:</p>
  
  <pre><code>library(ggplot2)
  dat &lt;- data.frame(x = rnorm(100000, 0, 5), y = rnorm(100000, 0, 5), z = rnorm(100000, 42, 42))
  
  hexHist = ggplot(dat, aes(x, y, z = z)) + 
      stat_binhex(bins = 10) +
      stat_summary_hex(aes(label=..value..), bins = 10,
                       fun = function(z) {
                           (round(sum(z)/length(z), 0))
                       },
                       geom = "text")
  </code></pre>
  
  <p>But, when I change <code>stat_binhex</code> to <code>stat_bin2d</code> and <code>stat_summary_hex</code> to <code>stat_summary_2d</code>, I get the following error:</p>
  
  <blockquote>
    <p><code>geom_text</code> requires the following missing aesthetics: x, y</p>
  </blockquote>
  
  <p>Explicitly adding the arguments <code>x = dat$x</code> and <code>y = dat$y</code> to <code>aes</code> doesn't change anything. Why isn't <code>stat_summary_hex</code> seeing the columns?</p>