title: p2.inf Filtering in Tycho when building an RCP application
body: <p>I´m building an RCP application using tycho. The RCP application uses p2 and its self updateable capabilities configuring the respository in an p2.inf file. Works like a charm.</p>
  
  <p>Now I want to introduce a placeholder ${updatesiteurl} in the p2.inf file and replace it with the URL according to the environment for which it is built. But unforunately it get´s replaced with an empty string instead of the environment variable which I guess happens because tycho, or the p2 director, replaces some escaped characters (like the ":" which is ${58} for example).</p>
  
  <p>Any ideas how this could be solved? I thought about explicitly declaring the resource plugin and binding it to an earlier build phase but that didn´t work either...</p>