Tighten up Windows CRLF conversion in our TAP test scripts.

The previous approach was to search-and-destroy all \r occurrences
no matter what.  That seems more likely to hide bugs than anything
else; indeed it seems to be hiding one now.  Fix things so that
we only transform \r\n to \n.

Side effects: must do this before, not after, chomp'ing if we're
going to chomp, else we'd fail to clean up a trailing \r\n.  Also,
remove safe_psql's redundant repetition of what psql already did;
else it might reduce \r\r\n to \n, which is exactly the scenario
I'm hoping to expose.

Perhaps this should be back-patched, but for now I'm content to
see what happens in HEAD.

Discussion: https://postgr.es/m/412ae8da-76bb-640f-039a-f3513499e53d@gmx.net

src/bin/pg_rewind/t/RewindTest.pm

@@ -112,7 +112,7 @@ sub check_query
 	}
 	else
 	{
-		$stdout =~ s/\r//g if $Config{osname} eq 'msys';
+		$stdout =~ s/\r\n/\n/g if $Config{osname} eq 'msys';
 		is($stdout, $expected_stdout, "$test_name: query result matches");
 	}
 	return;