title: GGplot custom scale transformation with custom ticks
body: <p>I'm attempting to use a custom scale/axis transformation, like so:</p>
  
  <pre><code>library(ggplot2)
  library(scales)
  
  dat &lt;- data.frame(
    time.tot = c(407.17, 168.83, 127.8, 108.88, 69.04, 68.5, 59.76, 407.17, 
                 168.83, 127.8, 108.88, 69.04, 68.5, 59.76, 407.17, 168.83, 127.8, 
                 108.88, 69.04, 68.5, 59.76),
    error = c(0, 0.01, 0.05, 0.1, 0.5, 0.7, 1, 1.91e-06, 0.00229, 0.00884, 
              0.0172, 0.128, 0.128, 0.22, 1.43e-08, 0.000337, 0.00121, 0.00221, 
              0.0123, 0.0123, 0.0213, 0, 0.01, 0.05, 0.1, 0.5, 0.7, 1, 1.91e-06, 
              0.00229, 0.00884, 0.0172, 0.128, 0.128, 0.22, 1.43e-08, 0.000337, 
              0.00121, 0.00221, 0.0123, 0.0123, 0.0213),
    type = rep(c("A", "B", "C"), each=7))
  
  eps &lt;- 1e-8
  tn &lt;- trans_new("logpeps",
                  function(x) log(x+eps),
                  function(y) exp(y)-eps,
                  domain=c(0, Inf),
                  breaks=c(0, 0.1, 1))
  
  ggplot(dat, aes(x=time.tot, y=error, color=type)) +
    geom_line() + geom_point() + coord_trans(y = tn)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/d7IM5.png" rel="noreferrer"><img src="https://i.stack.imgur.com/d7IM5.png" alt="enter image description here"></a></p>
  
  <p>As you can see, the y-axis is indeed transformed by my specified function, <code>y=log(x+eps)</code>.  The <code>breaks</code> argument isn't having any effect though.  I'm sure I'm specifying it wrong, but I haven't been able to figure out from the docs how to make it work.  Any suggestions?</p>
  
  <p>I'm also wondering how/whether to "fix" the curvy lines - looks like they're drawn in the original scale and then transformed using my custom <code>tn</code> afterwards.</p>