title: geom_bar in ggplot produces error with ?geom_bar example
body: <p>The following example comes straight from the help page <code>?geom_bar</code>:</p>
  
  <pre><code>g &lt;- ggplot(mpg, aes(class))
  g + geom_bar()
  </code></pre>
  
  <p>This gives <code>Error: Aesthetics must be either length 1 or the same as the data (7): width</code> 
  with traceback:</p>
  
  <pre><code>11: stop("Aesthetics must be either length 1 or the same as the data (", 
          n, "): ", paste(names(!good), collapse = ", "), call. = FALSE)
  10: check_aesthetics(params[aes_params], nrow(data))
  9: f(..., self = self)
  8: self$geom$use_defaults(data, self$aes_params)
  7: f(..., self = self)
  6: l$compute_geom_2(d)
  5: f(l = layers[[i]], d = data[[i]])
  4: by_layer(function(l, d) l$compute_geom_2(d))
  3: ggplot_build(x)
  2: print.ggplot(x)
  1: function (x, ...) 
     UseMethod("print")(x)
  </code></pre>
  
  <p>Is this a bug, a conflicting package or something else? </p>
  
  <p>Session info below.</p>
  
  <pre><code>R version 3.3.3 (2017-03-06)
  Platform: x86_64-pc-linux-gnu (64-bit)
  Running under: Linux Mint 18.1
  
  locale:
   [1] LC_CTYPE=C                 LC_NUMERIC=C               LC_TIME=C                  LC_COLLATE=C               LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C                 
   [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
  
  attached base packages:
  [1] parallel  grid      stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
   [1] doParallel_1.0.10  iterators_1.0.8    crunch_0.1.0       data.table_1.10.4  bit64_0.9-5        tabplot_1.3-2      ffbase_0.12.3      ff_2.2-13          bit_1.1-12         descr_1.1.3        zoo_1.7-14         forcats_0.2.0     
  [13] testthat_1.0.2     knitr_1.15.1       foreach_1.4.3      scales_0.4.1       viridis_0.3.4      d3heatmap_0.6.1.1  leaflet_1.1.0      highcharter_0.5.0  gridExtra_2.2.1    ggfortify_0.4.1    ggiraphExtra_0.1.0 ggplot2_2.2.1     
  [25] magrittr_1.5       lubridate_1.6.0    stringr_1.2.0      ineq_0.2-13        DT_0.2             flexdashboard_0.5  extrafont_0.17     HDoutliers_0.15    mclust_5.2.3       FactoMineR_1.35    FNN_1.1            vcdExtra_0.7-0    
  [37] gnm_1.0-8          vcd_1.4-3          foreign_0.8-67     readxl_0.1.1       uuid_0.1-2         openxlsx_4.0.0    
  
  loaded via a namespace (and not attached):
   [1] nlme_3.1-131         xts_0.9-7            rprojroot_1.2        tools_3.3.3          backports_1.0.5      R6_2.2.0             DBI_0.6              lazyeval_0.2.0       mgcv_1.8-16          colorspace_1.3-2     nnet_7.3-12         
  [12] mnormt_1.5-5         compiler_3.3.3       extrafontdb_1.0      flashClust_1.01-2    xml2_1.1.1           officer_0.1.1        labeling_0.3         lmtest_0.9-35        psych_1.6.12         digest_0.6.12        relimp_1.0-5        
  [23] rmarkdown_1.3        R.utils_2.5.0        ca_0.70              base64enc_0.1-3      htmltools_0.3.5      rvg_0.1.3            htmlwidgets_0.8      TTR_0.23-1           quantmod_0.4-7       shiny_1.0.0          jsonlite_1.3        
  [34] crosstalk_1.0.0      dplyr_0.5.0          R.oo_1.21.0          rlist_0.4.6.1        leaps_3.0            qvcalc_0.9-0         Matrix_1.2-8         Rcpp_0.12.10         munsell_0.4.3        gdtools_0.1.4        R.methodsS3_1.7.1   
  [45] scatterplot3d_0.3-38 stringi_1.1.2        MASS_7.3-45          plyr_1.8.4           crayon_1.3.2         lattice_0.20-34      igraph_1.0.1         codetools_0.2-15     reshape2_1.4.2       fastmatch_1.1-0      ggiraph_0.3.2       
  [56] evaluate_0.10        mycor_0.1            png_0.1-7            httpuv_1.3.3         Rttf2pt1_1.3.4       gtable_0.2.0         purrr_0.2.2          tidyr_0.6.1          assertthat_0.1       mime_0.5             xtable_1.8-2        
  [67] broom_0.4.2          tibble_1.2           cluster_2.0.6    
  </code></pre>