Error return code for io_reload_data()

The return code from new_data() and io_load_data() is explicitly defined as a
bit mask. A file access error is recognised and reported back to the user.

Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/calcurse.h

@@ -673,7 +673,8 @@ enum {
 	IO_RELOAD_CTINUE,
 	IO_RELOAD_MERGE,
 	IO_RELOAD_CANCEL,
-	IO_RELOAD_NOOP
+	IO_RELOAD_NOOP,
+	IO_RELOAD_ERROR
 };
 
 /* Week days. */