Use non-deprecated ways to get a default user agent.

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/branches/Temp_API_Finalization@387522 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/fop/apps/Fop.java

 
         foUserAgent = ua;
         if (foUserAgent == null) {
-            foUserAgent = new FOUserAgent();
+            foUserAgent = FopFactory.newInstance().newFOUserAgent();
         }
         
         this.stream = stream;
 
         foUserAgent = ua;
         if (foUserAgent == null) {
-            foUserAgent = new FOUserAgent();
+            foUserAgent = FopFactory.newInstance().newFOUserAgent();
         }
         
         createDefaultHandler();
      */
     public Fop(String outputFormat) {
         this.outputFormat = outputFormat;
-        foUserAgent = new FOUserAgent();
+        foUserAgent = FopFactory.newInstance().newFOUserAgent();
     }
 
     /**