KT-1996 Missing ABSTRACT_MEMBER_NOT_IMPLEMENTED when two supertypes contains same abstract member

===
trait Foo {
    fun foo(): Unit
}

trait Bar {
    fun foo(): Unit
}

class Baz : Foo, Bar // no error here
===

#KT-1996 fixed

compiler/frontend/src/org/jetbrains/jet/lang/resolve/OverrideResolver.java

@@ -307,14 +307,19 @@ public class OverrideResolver {
             else {
                 List<CallableMemberDescriptor> nonAbstractManyImpl = Lists.newArrayList();
                 Set<CallableMemberDescriptor> filteredOverriddenDeclarations = OverridingUtil.filterOverrides(Sets.newHashSet(overriddenDeclarations));
+                boolean allSuperAbstract = true;
                 for (CallableMemberDescriptor overridden : filteredOverriddenDeclarations) {
                     if (overridden.getModality() != Modality.ABSTRACT) {
                         nonAbstractManyImpl.add(overridden);
+                        allSuperAbstract = false;
                     }
                 }
                 if (nonAbstractManyImpl.size() > 1) {
                     manyImpl.addAll(nonAbstractManyImpl);
                 }
+                else if (allSuperAbstract) {
+                    abstractNoImpl.addAll(overriddenDeclarations);
+                }
             }
         }
     }

compiler/testData/diagnostics/tests/override/MultipleDefaultsInSupertypesNoExplicitOverride.jet

@@ -6,5 +6,5 @@ trait Y {
     fun foo(a : Int = 1)
 }
 
-class <!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE!>Z1<!> : X, Y {} // BUG
-object <!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE!>Z1O<!> : X, Y {} // BUG
+class <!ABSTRACT_MEMBER_NOT_IMPLEMENTED, MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE!>Z1<!> : X, Y {} // BUG
+object <!ABSTRACT_MEMBER_NOT_IMPLEMENTED, MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE!>Z1O<!> : X, Y {} // BUG

compiler/testData/diagnostics/tests/override/ToAbstractMembersFromSuper-kt1996.jet

@@ -0,0 +1,11 @@
+// http://youtrack.jetbrains.com/issue/KT-1996
+
+trait Foo {
+    fun foo(): Unit
+}
+
+trait Bar {
+    fun foo(): Unit
+}
+
+class <!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>Baz<!> : Foo, Bar