Add MessageCollector#hasErrors, get rid of MessageSeverityCollector

Also fix duplicated wrapping of a message collector into a message severity
collector (in CLICompiler and in the beginning of doExecute in
K2JVMCompiler/K2JSCompiler)

compiler/tests/org/jetbrains/kotlin/modules/xml/AbstractModuleXmlParserTest.java

@@ -33,7 +33,7 @@ import java.io.IOException;
 
 public abstract class AbstractModuleXmlParserTest extends TestCase {
 
-    protected void doTest(String xmlPath) throws IOException {
+    protected static void doTest(String xmlPath) throws IOException {
         File txtFile = new File(FileUtil.getNameWithoutExtension(xmlPath) + ".txt");
 
         ModuleScriptData result = ModuleXmlParser.parseModuleScript(xmlPath, new MessageCollector() {
@@ -43,6 +43,11 @@ public abstract class AbstractModuleXmlParserTest extends TestCase {
             ) {
                 throw new AssertionError(MessageRenderer.PLAIN_FULL_PATHS.render(severity, message, location));
             }
+
+            @Override
+            public boolean hasErrors() {
+                throw new UnsupportedOperationException();
+            }
         });
 
         StringBuilder sb = new StringBuilder();