Generate bridges for trait implementations properly

The intent was to keep the bridge codegen model as simple as possible: we
should be able to figure out all necessary bridges only by a minimal interface
that FunctionHandle provides (isAbstract, isDeclaration, getOverridden)

Add different tests for bridges

 #KT-318 Obsolete

core/descriptors/src/org/jetbrains/jet/lang/resolve/OverridingUtil.java

@@ -318,7 +318,8 @@ public class OverridingUtil {
      *
      * @see CallableMemberDescriptor.Kind#isReal()
      */
-    public static Collection<CallableMemberDescriptor> getOverriddenDeclarations(CallableMemberDescriptor descriptor) {
+    @NotNull
+    public static Collection<CallableMemberDescriptor> getOverriddenDeclarations(@NotNull CallableMemberDescriptor descriptor) {
         Map<ClassDescriptor, CallableMemberDescriptor> result = Maps.newHashMap();
         getOverriddenDeclarations(descriptor, result);
         return result.values();