Added printf format checking to logging function.

This also required changing the logging of "" at the
start of each test to appeal the otherwise-friendly
compiler.

test-tool/test_write10_beyond_eol.c

@@ -36,7 +36,7 @@ test_write10_beyond_eol(void)
 		return;
 	}
 
-	logging(LOG_VERBOSE, "");
+	logging(LOG_VERBOSE, LOG_BLANK_LINE);
 	logging(LOG_VERBOSE, "Test WRITE10 1-256 blocks one block beyond the end");
 	for (i = 1; i <= 256; i++) {
 		unsigned char *buf = malloc(block_size * i);