enhance tests (mostly codegen)

* drop dependency on stdlib/alt-headers in the most tests
* assign to myEnvironment at most once in JetLiteFixture
* more tests do not compile runtime

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

@@ -19,6 +19,7 @@ package org.jetbrains.jet.codegen;
 import jet.IntRange;
 import jet.Tuple2;
 import jet.Tuple4;
+import org.jetbrains.jet.lang.resolve.java.CompilerSpecialMode;
 
 import java.awt.*;
 import java.lang.reflect.InvocationTargetException;
@@ -30,6 +31,13 @@ import java.util.Arrays;
  * @author yole
  */
 public class NamespaceGenTest extends CodegenTestCase {
+
+    @Override
+    protected void setUp() throws Exception {
+        super.setUp();
+        createEnvironmentWithMockJdk(CompilerSpecialMode.JDK_HEADERS);
+    }
+
     public void testPSVM() throws Exception {
         loadFile("PSVM.jet");
 //        System.out.println(generateToText());