Fix JUnit imports in SourceHttpMessageConverterTests

When org.junit.Assert.* is statically imported, the class does not
compile in Eclipse/STS since XMLAssert extends junit.framework.Assert.

spring-web/src/test/java/org/springframework/http/converter/xml/SourceHttpMessageConverterTests.java

@@ -45,8 +45,9 @@ import org.springframework.http.MockHttpOutputMessage;
 import org.springframework.util.FileCopyUtils;
 
 import static org.custommonkey.xmlunit.XMLAssert.*;
+// Do NOT statically import org.junit.Assert.*, since XMLAssert extends junit.framework.Assert
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertTrue;
 
 /**