Getter and setter methods not generated for Optional NTAs in asbstract AST classes

[Jesper Öqvist]

Example AST specification:

abstract A ::= /[B]/;

If A were not abstract then JastAdd would generate the methods getA and setA. The getter and setter methods should be generated for the class even if it is declared abstract.

[Niklas Fors]

This works fine in JastAdd2 2.1.1-10-gf149616.