Java 8 rules for method overrides:

- base class method wins against a (default) interface method,
so an abstract base class method should always be implemented
in a derived class;

- interface methods clash regardless of abstract/default
with possibly undefined behavior at run-time,
so a class or interface should always define its own method
for methods inherited from multiple interfaces and not from base class;

- meaningful diagnostics for class inheriting conflicting JVM signatures.
Since no override will happen under Java 8 rules,
ACCIDENTAL_OVERRIDE is misleading for this case;

- update testData.

compiler/testData/diagnostics/tests/declarationChecks/kt559.kt

@@ -14,17 +14,17 @@ abstract class D(): A() {
     override val i : Int = 34
 }
 
-<!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>class C<!>() : D() {
+<!ABSTRACT_CLASS_MEMBER_NOT_IMPLEMENTED!>class C<!>() : D() {
     fun test() {
         super.i
     }
 }
 
-<!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>class B<!>() : A() {
+<!ABSTRACT_CLASS_MEMBER_NOT_IMPLEMENTED!>class B<!>() : A() {
     override fun foo(): Int {
         super.<!ABSTRACT_SUPER_CALL!>i<!>
 
         super.fff() //everything is ok
         return super.<!ABSTRACT_SUPER_CALL!>foo<!>()  //no error!!
     }
-}
+}