Actually create .kt files in the file system for Kotlin multifile tests

compiler/tests/org/jetbrains/jet/checkers/KotlinMultiFileTestWithWithJava.java

@@ -99,6 +99,7 @@ public abstract class KotlinMultiFileTestWithWithJava<M, F> extends JetLiteFixtu
     protected void doTest(String filePath) throws Exception {
         File file = new File(filePath);
         final File javaFilesDir = createJavaFilesDir();
+        final File kotlinFilesDir = getKotlinSourceRoot();
 
         String expectedText = JetTestUtils.doLoadFile(file);
 
@@ -117,6 +118,10 @@ public abstract class KotlinMultiFileTestWithWithJava<M, F> extends JetLiteFixtu
                             writeSourceFile(fileName, text, javaFilesDir);
                         }
 
+                        if (fileName.endsWith(".kt") && kotlinFilesDir != null) {
+                            writeSourceFile(fileName, text, kotlinFilesDir);
+                        }
+
                         return createTestFile(module, fileName, text, directives);
                     }