This patch adds a --stdout=line|unbuf option that lets the
user change the buffering of stdout.

To use this patch, run these commands for a successful build:

    patch -p1 <patches/stdout.diff
    ./configure                            (optional if already run)
    make

based-on: a01e3b490eb36ccf9e704840e1b6683dab867550
diff --git a/options.c b/options.c
--- a/options.c
+++ b/options.c
@@ -301,6 +301,7 @@ static int refused_partial, refused_progress, refused_delete_before;
 static int refused_delete_during;
 static int refused_inplace, refused_no_iconv;
 static BOOL usermap_via_chown, groupmap_via_chown;
+static char *stdout_buffering;
 static char *bwlimit_arg, *max_size_arg, *min_size_arg;
 static char tmp_partialdir[] = ".~tmp~";
 
@@ -776,6 +777,7 @@ void usage(enum logcode F)
   rprintf(F,"     --password-file=FILE    read daemon-access password from FILE\n");
   rprintf(F,"     --list-only             list the files instead of copying them\n");
   rprintf(F,"     --bwlimit=RATE          limit socket I/O bandwidth\n");
+  rprintf(F,"     --stdout=line|unbuf     change buffering of stdout\n");
   rprintf(F,"     --write-batch=FILE      write a batched update to FILE\n");
   rprintf(F,"     --only-write-batch=FILE like --write-batch but w/o updating destination\n");
   rprintf(F,"     --read-batch=FILE       read a batched update from FILE\n");
@@ -1008,6 +1010,7 @@ static struct poptOption long_options[] = {
   {"password-file",    0,  POPT_ARG_STRING, &password_file, 0, 0, 0 },
   {"blocking-io",      0,  POPT_ARG_VAL,    &blocking_io, 1, 0, 0 },
   {"no-blocking-io",   0,  POPT_ARG_VAL,    &blocking_io, 0, 0, 0 },
+  {"stdout",           0,  POPT_ARG_STRING, &stdout_buffering, 0, 0, 0 },
   {"remote-option",   'M', POPT_ARG_STRING, 0, 'M', 0, 0 },
   {"protocol",         0,  POPT_ARG_INT,    &protocol_version, 0, 0, 0 },
   {"checksum-seed",    0,  POPT_ARG_INT,    &checksum_seed, 0, 0, 0 },
@@ -1793,6 +1796,13 @@ int parse_arguments(int *argc_p, const char ***argv_p)
 		}
 	}
 
+	if (stdout_buffering && !am_server) {
+		if (*stdout_buffering == 'u')
+			setvbuf(stdout, NULL, _IONBF, 0);
+		else
+			setvbuf(stdout, NULL, _IOLBF, 0);
+	}
+
 	if (human_readable > 1 && argc == 2 && !am_server) {
 		/* Allow the old meaning of 'h' (--help) on its own. */
 		usage(FINFO);