Allow for merging data files when reloading

This allows for merging the (unsaved) items with the items from the data
files when invoking the reload operation. To this end, an external merge
tool (defaults to vimdiff) is used.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/args.c

@@ -707,8 +707,8 @@ int parse_args(int argc, char **argv)
 				io_load_app();
 				io_load_todo();
 				io_import_data(IO_IMPORT_ICAL, ifile);
-				io_save_apts();
-				io_save_todo();
+				io_save_apts(path_apts);
+				io_save_todo(path_todo);
 				non_interactive = 1;
 			}
 			if (xflag) {