Checks if item is in the selection.
This function returns for the given path, if it is fully, partially or not part of the list of selected files. IsSubItemOf is set to true, if the given path is selected, because one of its parent folders is part of the list of selected paths. bIsSubItemOf is set to false, if the given path is included itself in the list of selected paths. Pass a dummy variable of type Boolean as second parameter to this method, if you do not need this information.
