Add register_column_headers() and print_column_headers() to deprecated.php to...

Add register_column_headers() and print_column_headers() to deprecated.php to prevent fatal errors in plugins. See #14579

git-svn-id: https://core.svn.wordpress.org/trunk@15510 1a063a9b-81f0-0310-95a4-ce76da25c4cd