Lua: errors vs messages

[Bart Bogaerts]

Currently in idp_intern.idp, we are often writing messages like

        io.stderr:write("Error: structure expected\n")

Is there a reason for not using the error method from lua? I.e., do we want our tools to continue after such an error is encountered???

Can easily be updated to decent error messages. Also "structure expected" is maybe a bit vague. Some more context is often useful. (which user call caused the error)