ObjC: improve debugging in Xcode with the test script

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
ObjC: prepared to handle multiple input files

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
ObjC: improved tree walking algorithms

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>