Add section order check in util/find-doc-nits

This patch checks if the EXAMPLES section in a pod file is placed
before the RETURN VALUES section.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

(cherry picked from commit cc838ee2d66f7295bf7a7e6695aab1080d6791e9)
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NMatthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/8736)

util/find-doc-nits

@@ -137,6 +137,18 @@ sub name_synopsis()
     }
 }
 
+# Check if EXAMPLES is located after RETURN VALUES section.
+sub check_example_location()
+{
+    my $filename = shift;
+    my $contents = shift;
+
+    return unless $contents =~ /=head1 RETURN VALUES/
+        and $contents =~ /=head1 EXAMPLES/;
+    print "$filename: RETURN VAULES should be placed before EXAMPLES section\n"
+        if $contents =~ /=head1 EXAMPLES.*=head1 RETURN VALUES/ms;
+}
+
 sub check()
 {
     my $filename = shift;
@@ -150,6 +162,8 @@ sub check()
         close POD;
     }
 
+    &check_example_location($filename, $contents) if $filename =~ m|man3/|;
+
     my $id = "${filename}:1:";
 
     &name_synopsis($id, $filename, $contents)