title: geom_point and coord_polar - Warning for unknown aesthetics
body: <p>I know geom_point doesn't have mapping for ymin and ymax, but when I don't use them it doesn't give the figure I expect. Nevertheless when using ymin and ymax I get the figure I wish, but I get warning of "Ignoring unknown aesthetics: ymin, ymax". I can't figure out what should be done to avoid warning but getting the plot I wish.</p>
  
  <p>Here is example dataset:</p>
  
  <pre><code>ab &lt;- data.frame(a = seq(50,100,by=10), b=LETTERS[1:6])
  </code></pre>
  
  <p>Without ymin and ymax but not the figure I expect:</p>
  
  <pre><code>library("ggplot2")
  
  ggplot(ab) +
    scale_x_discrete() +
      scale_y_reverse() +
    geom_rect(xmin=Inf, xmax = -Inf, ymin = 0 - 50, ymax = 0, fill="lightblue") +
    geom_rect(xmin=Inf, xmax = -Inf, ymin = 0 - 82, ymax = 0 - 50, fill="lightgreen") +
    geom_rect(xmin=Inf, xmax = -Inf, ymin = -100, ymax = 0 - 80, fill="darkgreen") +
    geom_vline(xintercept=1:6, size=1.5, color="white") +
    geom_hline(yintercept=c(50, 80, 100), size=0.1, color="white") +
    geom_point(aes(x=b, y=a),
               shape=21, fill="#FF9933", size=10, position="identity") +
    ggtitle("Test") +
    coord_polar() +
    theme(
      plot.title=element_text(face = "bold", color = "black", size = 17, ),
      panel.background=element_rect(fill = c("white")),
      panel.grid=element_blank(),
      panel.grid.major=element_line(size=2),
      panel.grid.minor.y=element_blank(),
      axis.text.x=element_text(vjust=5),
      axis.text=element_text(size = 12, color = "black", face = "bold"),
      axis.text.y=element_blank(),
      axis.title.x=element_blank(),
      axis.title.y=element_blank(),
      axis.ticks=element_blank())
  </code></pre>
  
  <p>with ymin and ymax in geom_point (the expected output with warning):</p>
  
  <pre><code>ggplot(ab) +
    scale_x_discrete() +
      scale_y_reverse() +
    geom_rect(xmin=Inf, xmax = -Inf, ymin = 0 - 50, ymax = 0, fill="lightblue") +
    geom_rect(xmin=Inf, xmax = -Inf, ymin = 0 - 82, ymax = 0 - 50, fill="lightgreen") +
    geom_rect(xmin=Inf, xmax = -Inf, ymin = -100, ymax = 0 - 80, fill="darkgreen") +
    geom_vline(xintercept=1:6, size=1.5, color="white") +
    geom_hline(yintercept=c(50, 80, 100), size=0.1, color="white") +
    geom_point(aes(x=b, y=a, ymin = 0, ymax = 100),
               shape=21, fill="#FF9933", size=10, position="identity") +
    ggtitle("Test") +
    coord_polar() +
    theme(
      plot.title=element_text(face = "bold", color = "black", size = 17, ),
      panel.background=element_rect(fill = c("white")),
      panel.grid=element_blank(),
      panel.grid.major=element_line(size=2),
      panel.grid.minor.y=element_blank(),
      axis.text.x=element_text(vjust=5),
      axis.text=element_text(size = 12, color = "black", face = "bold"),
      axis.text.y=element_blank(),
      axis.title.x=element_blank(),
      axis.title.y=element_blank(),
      axis.ticks=element_blank())
  </code></pre>