Add test for postgresql.conf.sample line syntax

All GUCs in postgresql.conf.sample should be set to the default
value and be commented out.  This syntax was however not tested
for, making omissions easy to miss.  Add a test which check all
lines for syntax.

Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://postgr.es/m/19727040-3EE4-4719-AF4F-2548544113D7@yesql.se

src/test/modules/test_misc/t/003_check_guc.pl

@@ -56,7 +56,7 @@ while (my $line = <$contents>)
 	# file.
 	# - Valid configuration options are followed immediately by " = ",
 	# with one space before and after the equal sign.
-	if ($line =~ m/^#?([_[:alnum:]]+) = .*/)
+	if ($line =~ m/^#([_[:alnum:]]+) = .*/)
 	{
 		# Lower-case conversion matters for some of the GUCs.
 		my $param_name = lc($1);
@@ -69,7 +69,12 @@ while (my $line = <$contents>)
 		# Update the list of GUCs found in the sample file, for the
 		# follow-up tests.
 		push @gucs_in_file, $param_name;
+
+		next;
 	}
+	# Make sure each line starts with either a # or whitespace
+	fail("$line missing initial # in postgresql.conf.sample")
+	  if $line =~ /^\s*[^#\s]/;
 }
 
 close $contents;