Loads a DCL file
(load_dialog dclfile)
The load_dialog function searches for files according to the AutoCAD library search path.
This function is the complement of unload_dialog. An application can load multiple DCL files with multiple load_dialog calls.
A positive integer value (dcl_id) if successful, or a negative integer if load_dialog can't open the file. The dcl_id is used as a handle in subsequent new_dialog and unload_dialog calls.