turn maildir_again() into a proper varargs function

this is mostly to work around the fact that both gcc and clang won't
accept the format string declaration (i.e., will complain with
-Wformat-nonliteral) if the *called* function does not actually take a
va_list.

on the upside, it makes one caller cleaner. yay ...

src/common.h

@@ -130,6 +130,7 @@ void ATTR_PRINTFLIKE(1, 2) progress( const char *, ... );
 void ATTR_PRINTFLIKE(1, 2) notice( const char *, ... );
 void ATTR_PRINTFLIKE(1, 2) warn( const char *, ... );
 void ATTR_PRINTFLIKE(1, 2) error( const char *, ... );
+void ATTR_PRINTFLIKE(1, 0) vsys_error( const char *, va_list va );
 void ATTR_PRINTFLIKE(1, 2) sys_error( const char *, ... );
 void flushn( void );
 

src/drv_maildir.c

@@ -1510,14 +1510,16 @@ maildir_rescan( maildir_store_t *ctx )
 	return DRV_OK;
 }
 
-static int
-maildir_again( maildir_store_t *ctx, maildir_message_t *msg,
-               const char *err, const char *fn, const char *fn2 )
+static int ATTR_PRINTFLIKE(3, 0)
+maildir_again( maildir_store_t *ctx, maildir_message_t *msg, const char *err, ... )
 {
 	int ret;
 
 	if (errno != ENOENT) {
-		sys_error( err, fn, fn2 );
+		va_list va;
+		va_start( va, err );
+		vsys_error( err, va );
+		va_end( va );
 		return DRV_BOX_BAD;
 	}
 	if ((ret = maildir_rescan( ctx )) != DRV_OK)
@@ -1539,7 +1541,7 @@ maildir_fetch_msg( store_t *gctx, message_t *gmsg, msg_data_t *data,
 		nfsnprintf( buf, sizeof(buf), "%s/%s/%s", ctx->path, subdirs[gmsg->status & M_RECENT], msg->base );
 		if ((fd = open( buf, O_RDONLY )) >= 0)
 			break;
-		if ((ret = maildir_again( ctx, msg, "Cannot open %s", buf, 0 )) != DRV_OK) {
+		if ((ret = maildir_again( ctx, msg, "Cannot open %s", buf )) != DRV_OK) {
 			cb( ret, aux );
 			return;
 		}

src/util.c

@@ -149,19 +149,26 @@ error( const char *msg, ... )
 }
 
 void
-sys_error( const char *msg, ... )
+vsys_error( const char *msg, va_list va )
 {
-	va_list va;
 	char buf[1024];
 
 	flushn();
-	va_start( va, msg );
 	if ((uint)vsnprintf( buf, sizeof(buf), msg, va ) >= sizeof(buf))
 		oob();
-	va_end( va );
 	perror( buf );
 }
 
+void
+sys_error( const char *msg, ... )
+{
+	va_list va;
+
+	va_start( va, msg );
+	vsys_error( msg, va );
+	va_end( va );
+}
+
 void
 add_string_list_n( string_list_t **list, const char *str, int len )
 {