title: Namespace issue with raster package plot function?
body: <p>I have experiencing a weird problem with the 'plot' function of the 'raster' package. </p>
  
  <pre><code>library(raster)
  ras &lt;- raster(ncol=10, nrow=10)
  </code></pre>
  
  <p>EDIT</p>
  
  <pre><code>values(ras) &lt;- runif(ncell(ras))
  </code></pre>
  
  <p>END EDIT</p>
  
  <pre><code>plot(ras)
  
  Erreur dans as.double(y) : 
  cannot coerce type 'S4' to vector of type 'double'
  </code></pre>
  
  <p>For what I have read on the net, this error depends on the user, and probably depends on the loaded packages. In my case, the problem comes from the fact that r uses the standard 'plot' method from the 'graphics' package, when it should use the specific 'raster' method since 'ras' is a rasterLayer object. However, for a reason I do not understand, 'plot' is not imported in the 'raster' namespace, while all the other functions are. </p>
  
  <pre><code>&gt; raster::plot
  Erreur : 'plot' n'est pas un objet exporté depuis 'namespace:raster'
  </code></pre>
  
  <p>To be compared with :    </p>
  
  <pre><code>raster::persp
  standardGeneric for "persp" defined from package "graphics"
  function (x, ...) 
  standardGeneric("persp")
  &lt;environment: 0x0cd9eb80&gt;
  Methods may be defined for arguments: x
  Use  showMethods("persp")  for currently available ones.
  </code></pre>
  
  <p>Since I do not completely understand how namespaces behave, I am looking for your help ! Is this kind of situation familiar for you, and do you have a way to solve it ? In the meantime, do you know a function to display the content of a namespace (so I could check the content of the raster namespace step by step) ?</p>
  
  <p>PS: I am using R 2.15.2 with RStudio, many packages loaded but all are up to date.</p>
  
  <pre><code>sessionInfo()
  R version 2.15.0 (2012-03-30)
  Platform: i386-pc-mingw32/i386 (32-bit)
  
  locale:
  [1] LC_COLLATE=French_Belgium.1252  LC_CTYPE=French_Belgium.1252          LC_MONETARY=French_Belgium.1252 LC_NUMERIC=C                   
  [5] LC_TIME=French_Belgium.1252    
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] raster_2.0-41 sp_1.0-5     
  
  loaded via a namespace (and not attached):
   [1] grid_2.15.0      hexbin_1.26.0    intervals_0.13.3 lattice_0.20-6   rgdal_0.8-4      spacetime_1.0-3  spam_0.29-2      tools_2.15.0    
   [9] xts_0.9-2        zoo_1.7-9             
  </code></pre>
  
  <p>Thanks you,</p>
  
  <p>François</p>