title: Groovy's MarkupBuilder exception on generating "id" XML tag
body: <p>I'm trying to construct a XML feed, and Groovy's MarkupBuilder is giving me headaches:</p>
  
  <pre><code> def newsstandFeed(def id) {
      def publication = Publication.get(id)
      def issues = issueService.getActiveIssuesForPublication(publication)
      def updateDate = DateUtil.getRFC3339DateString(publication.lastIssueUpdate)
  
      def writer = new StringWriter()
      writer.write("&lt;?xml version=\"1.0\" encoding=\"UTF-8\"?&gt;\n")
      def xml = new MarkupBuilder(writer)
      xml.feed('xmlns':"http://www.w3.org/2005/Atom", 'xmlns:news':"http://itunes.apple.com/2011/Newsstand") {
          updated("${updateDate}")
          issues.each { issue -&gt;
              entry {
                  id (issue.id)
                  updated("${DateUtil.getRFC3339DateString(issue.lastUpdated)}")
                  published("${DateUtil.getRFC3339DateString(issue.releaseDate)}")
                  summary(issue.summary)
                  "news:cover_art_icons" {
                      "news:cover_art_icon" (size:"SOURCE", src:"${issue.cover.remotePath}")
                  }
              }
          }
      }
  
      return writer.toString()
  }
  </code></pre>
  
  <p>I get this exception:</p>
  
  <pre><code>Class groovy.lang.MissingMethodException 
  No signature of method: java.lang.String.call() is applicable for argument types: (org.codehaus.groovy.runtime.GStringImpl) values: [CYB_001] Possible solutions: wait(), any(), wait(long), any(groovy.lang.Closure), take(int), each(groovy.lang.Closure)
  </code></pre>
  
  <p>"CYB_001" is the first "id" attribute.</p>
  
  <p>If I rename "id" it to "ids" or anything else, it works, and returns a proper XML document:</p>
  
  <pre><code>            ....
              issues.each { issue -&gt;
              entry {
                  ids ("${issue.id}")
                  ...
  </code></pre>
  
  <p>Any ideas why this is happening, and how I can work around the problem? </p>
  
  <p>The environment is Grails 2.1.1 (so Groovy 1.8, I assume)</p>