title: runs in R but not Rscript
body: <p>Here is my script</p>
  
  <pre><code>library(Rcpp)
  library(inline)
  
  myroot2 &lt;- rcpp(signature(xs="numeric"), body='double x=as&lt;double&gt;(xs); return wrap(::sqrt(x));')
  print(myroot2(100))
  </code></pre>
  
  <p>If I source this script from R it runs just fine</p>
  
  <pre><code>&gt;source('test.R')
  Attaching package: ‘inline’
  
  The following object is masked from ‘package:Rcpp’:
  
  registerPlugin
  
  [1] 10
  </code></pre>
  
  <p>In batch mode</p>
  
  <pre><code>Rscript --verbose test.R
  running
  '/usr/local/share/bcbio/anaconda/lib/R/bin/R --slave --no-restore -- 
  file=test.R'
  
  
  Attaching package: ‘inline’
  
  The following object is masked from ‘package:Rcpp’:
  
  registerPlugin
  Error in signature(xs = "numeric") : could not find function 
  "signature"
  Calls: rcpp -&gt; cxxfunction
  Execution halted
  </code></pre>
  
  <p>How to fix this?</p>