Support SKIP_TXT directive in diagnostic tests

Don't render the whole 'kotlin' package in some tests, because test data will
change every time something is updated in built-ins

compiler/tests/org/jetbrains/kotlin/checkers/BaseDiagnosticsTest.java

@@ -235,7 +235,7 @@ public abstract class BaseDiagnosticsTest extends
 
     protected class TestFile {
         private final List<CheckerTestUtil.DiagnosedRange> diagnosedRanges = Lists.newArrayList();
-        private final String expectedText;
+        public final String expectedText;
         private final TestModule module;
         private final String clearText;
         private final JetFile jetFile;