changes headers_in and headers_out handling in mod_lua to map apr_table_t...

changes headers_in and headers_out handling in mod_lua to map apr_table_t instances as boxed pointers

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@737293 13f79535-47bb-0310-9956-ffa450edef68