- 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.
A non-abstract super-declaration is allowed to stand as 'an implementation' of
a fake override only if its visibility is not less than visibilities of all
other super-declarations
#KT-2491 Fixed
Some corner cases still remain: KotlinSignature, propagation, deserialized
delegates to Java interfaces
#KT-1239 Obsolete
#KT-1924 In Progress
#KT-2081 Fixed
Dmitry Petrov