title: trouble getting Date field on X axis using ggplot2
body: <pre><code>head(bktst.plotdata)   
     date      method  product type  actuals  forecast   residual   Percent_error month
  1 2012-12-31  bauwd   CUSTM  NET  194727.51  -8192.00 -202919.51       -104.21 Dec12
  2 2013-01-31  bauwd   CUSTM  NET  470416.27   1272.01 -469144.26        -99.73 Jan13
  3 2013-02-28  bauwd   CUSTM  NET  190943.57  -1892.45 -192836.02       -100.99 Feb13
  4 2013-03-31  bauwd   CUSTM  NET  -42908.91   2560.05   45468.96       -105.97 Mar13
  5 2013-04-30  bauwd   CUSTM  NET -102401.68 358807.48  461209.16       -450.39 Apr13
  6 2013-05-31  bauwd   CUSTM  NET -134869.73 337325.33  472195.06       -350.11 May13
  </code></pre>
  
  <p>I have been trying to plot my back test result using <code>ggplot2</code>. Given above a sample dataset. I have dates ranging from Dec2012 to Jul2013. 3 levels in 'method', 5 levels in 'product' and 2 levels in 'type'
  I tried this code, trouble is that R is not reading x-axis correct, on the X-axis I am getting 'Jan, feb, mar, apr, may,jun, jul, aug', instead I expect R to plot Dec-to-Jul </p>
  
  <pre><code>month.plot1 &lt;- ggplot(data=bktst.plotdata, aes(x= date, y=Percent_error, colour=method))
  facet4 &lt;- facet_grid(product~type,scales="free_y")
  title3 &lt;- ggtitle("Percent Error - Month-over-Month")
  xaxis2 &lt;- xlab("Date")
  yaxis3 &lt;- ylab("Error (%)")
  month.plot1+geom_line(stat="identity", size=1, position="identity")+facet4+title3+xaxis2+yaxis3
  
  # Tried changing the code to this still not getting the X-axis right
  month.plot1 &lt;- ggplot(data=bktst.plotdata, aes(x= format(date,'%b%y'), y=Percent_error, colour=method))
  month.plot1+geom_line(stat="identity", size=1, position="identity")+facet4+title3+xaxis2+yaxis3
  </code></pre>