title: escaping colon ":" in SpEL expression
body: <p>I am trying to build a url in a spring integration flow like shown:</p>
  
  <pre><code>&lt;int:header name="url" expression="${gateway.protocol}+'://'+${gateway.host}+':'+#{systemProperties['integration-test.port']}?:${gateway.port}+'/'+${gateway.context}" /&gt;
  </code></pre>
  
  <p>however I continuously get the following error:</p>
  
  <pre><code>SpelParseException: EL1041E:(pos 9): After parsing a valid expression, there is still more data in the expression: '':''
  </code></pre>
  
  <p>I have tried using \ and \\ and as you can see I have single quotes around it, which according the documentation here <a href="http://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/expressions.html" rel="nofollow">http://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/expressions.html</a> should be enough.</p>
  
  <p>any help would be much appreciated.</p>
  
  <p>thanks</p>