ffi: remove superfluous super-class

Already in ffi_base.nit

Signed-off-by: Jean Privat <jean@pryen.org>
parser: remove superfluous super-class in the AST

Signed-off-by: Jean Privat <jean@pryen.org>
modelbuilder: return early from build_classes in case of errors

Signed-off-by: Jean Privat <jean@pryen.org>
modelbuilder: check clash of ancestors

Signed-off-by: Jean Privat <jean@pryen.org>
tests: update error_inh_clash*

Signed-off-by: Jean Privat <jean@pryen.org>
tests: remove superfluous super-classes in some tests

Signed-off-by: Jean Privat <jean@pryen.org>
modelbuilder: Check superfluous superclasses

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add error_superclass_superfluous.nit

Signed-off-by: Jean Privat <jean@pryen.org>
Merge branch 'check_classes'