Match latest git's repo branch message.

packaging/nightly-rsync

@@ -40,7 +40,7 @@ if ($make_tar) {
     my $status = join('', <IN>);
     close IN;
     die "The checkout is not clean:\n", $status unless $status =~ /\nnothing to commit.+working directory clean/;
-    die "The checkout is not on the master branch.\n" unless $status =~ /^# On branch master\n/;
+    die "The checkout is not on the master branch.\n" unless $status =~ /^(?:# )?On branch master\n/;
     system "make $gen_target" and die "make $gen_target failed!\n";
 
     my @extra_files;