Added a getContentLength() method to URLConnection

This is particularly important if you want to get the number of bytes of a
resource loaded by the class loader:
  getClass().getResource("myFile").openConnection().getContentLength()

classpath/java/net/URLConnection.java

@@ -25,6 +25,10 @@ public abstract class URLConnection {
     return getInputStream();
   }
 
+  public int getContentLength() {
+    return -1;
+  }
+
   public InputStream getInputStream() throws IOException {
     throw new UnknownServiceException();
   }