Flush every line when using meta mode and no -j or with -B.

Otherwise the output is buffered and it appears that make is stuck on something
long-running.  This problem is not present with -j as it uses different
code that was already flushing.

Discussed with:	sjg
Approved by:	re (blanket, META_MODE)
Sponsored by:	EMC / Isilon Storage Division

contrib/bmake/meta.c

@@ -1547,6 +1547,7 @@ meta_compat_parent(void)
     while (fgets(buf, sizeof(buf), fp)) {
 	meta_job_output(NULL, buf, "");
 	printf("%s", buf);
+	(void)fflush(stdout);
     }
     fclose(fp);
 }