title: Copy subdirectories if they contain a specific file in Ant
body: <p>Really new to Ant and I have been trying to figure that out but could not...</p>
  
  <p>Let say I have a structure like that :</p>
  
  <pre>
  Root
  |-data
    |-dir1
       |-include.xml
       |-subdir1
         |-file1
         |-file2
         |-include.xml
       |-subdir2
    |--dir2
       |-file1
       |-include.xml
    |--dir3
    |--dir4
       |-file1
       |-include.xml
    |--dir5
  |-build.xml
  |-other files
  </pre>
  
  <p>I'd like to copy the files at the root (which is pretty simple filtering). But the the troubles come : I want to copy subdirectories of data only if they contain a file, here named include.xml. Here is what the destination folder should look like after copying </p>
  
  <pre>
  Root
  |-data
    |-dir1
       |-include.xml
       |-subdir1
         |-file1
         |-file2
         |-include.xml
    |--dir2
       |-file1
       |-include.xml
    |--dir4
       |-file1
       |-include.xml
  |-build.xml
  |-other files
  </pre>
  
  <p>As you can see, /data/dir3, /data/dir5 and /data/dir1/subdir1 have not been copied, because they did not contain the include.xml file.</p>
  
  <p>It might be simple but I could not find a way to do it, the property and available being set from what I understood globally ?</p>