Fixing [JACKSON-62], NPE with JsonMappingException, getMessage().

diff --git a/src/perf/TestJsonPerf.java b/src/perf/TestJsonPerf.java
index 229cfa2..231ee48 100644
--- a/src/perf/TestJsonPerf.java
+++ b/src/perf/TestJsonPerf.java
@@ -2,8 +2,7 @@
 
 import org.codehaus.jackson.*;
 import org.codehaus.jackson.io.IOContext;
-import org.codehaus.jackson.map.ObjectMapper;
-import org.codehaus.jackson.map.TreeMapper;
+import org.codehaus.jackson.map.*;
 import org.codehaus.jackson.util.BufferRecycler;
 
 // json.org's reference implementation