Implement simplification of ordinal case nodes if the case expression is constant (might be useful when inlining).

+ nset.pas, tcasenode: add simplify method; for ordinal constant case expressions either return a copy of the correct block or return a nothing node if the constant did not match anything

+ added test to check that nothing is broken


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@26824 3ad0048d-3df7-0310-abae-a5850022a9f2