BC412: add to backend_tcl; add skeleton test

GUI: allow for Qt not parsing #if's in slots (copy_to_clipboard_png())

backend/library.c

@@ -1871,6 +1871,7 @@ unsigned int ZBarcode_Cap(int symbol_id, unsigned int cap_flag) {
             case BARCODE_HIBC_128: /* See CODE128 */
             case BARCODE_HIBC_PDF: /* See PDF417 */
             case BARCODE_HIBC_MICPDF: /* See PDF417 */
+            case BARCODE_BC412: /* TODO: Find doc */
                 break;
             default:
                 result |= ZINT_CAP_COMPLIANT_HEIGHT;