Introduce CodegenStatementVisitor

Which will be used for generating statements (as opposed to generating
expressions always, as it is now)

Add StatementGenTest, which will check if we actually generate statements and
not expressions of type Unit, popping them off the stack later

compiler/tests/org/jetbrains/jet/codegen/StatementGenTest.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2010-2012 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.jet.codegen;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.jet.ConfigurationKind;
+
+public class StatementGenTest extends CodegenTestCase {
+    @Override
+    protected void setUp() throws Exception {
+        super.setUp();
+        createEnvironmentWithMockJdkAndIdeaAnnotations(ConfigurationKind.JDK_ONLY);
+    }
+
+    private void doTest() {
+        loadFile("statements/" + getTestName(true) + ".kt");
+        String text = generateToText();
+        // 'getstatic' means we refer to Unit.VALUE, which we shouldn't since these tests contain only statements
+        assertNoGetStatic(text);
+    }
+
+    private void assertNoGetStatic(@NotNull String text) {
+        assertFalse(text, text.toLowerCase().contains("getstatic"));
+    }
+}