tap: restore buffering to stdout

I noticed this when I straced something; we're doing 1-byte writes.
This reduced the time for "make check" from 12m37s to 11m48s.

ccan/tap/tap.c

@@ -260,7 +260,7 @@ _tap_init(void)
 		/* stdout needs to be unbuffered so that the output appears
 		   in the same place relative to stderr output as it does 
 		   with Test::Harness */
-		setbuf(stdout, 0);
+//		setbuf(stdout, 0);
 		run_once = 1;
 	}
 }

ccan/tap/test/run.c

@@ -66,8 +66,8 @@ int main(int argc, char *argv[])
 	int p[2];
 	int stdoutfd;
 
+	setbuf(stdout, 0);
 	printf("1..1\n");
-	fflush(stdout);
 	stderrfd = dup(STDERR_FILENO);
 	if (stderrfd < 0)
 		err(1, "dup of stderr failed");