This function can be used in order to append a Tcl Object at the end of
a valid Tcl List Object. The new element will be appended only if it is
not already contained in the list.
Return Value:
The return value from this function will be a standart Tcl completion
code (of type int) with one of the values TCL_OK and TCL_ERROR. If an
error occurs, the return value will be TCL_ERROR and an error message
describing the error will be left at the current Tcl interpreter
(CDM_Interp). If all annotators run without errors, TCL_OK will be
returned.