add Linktitle to Prev and Next Link

add_Linktitle.php

function add_rr_linktitle( $format, $link = FALSE ){
	if( $link )
	   $nex_prev = true;

	preg_match_all( '/<a href="(.*?)" rel="(.*?)">(.*?)<\/a>/', $format, $matches);
	return '<a href="' . $matches[1][0] . '" rel="' . $matches[2][0] . '"  title="' . get_adjacent_post( false, '', $nex_prev )->post_title . '">' . $matches[3][0] . '</a> ';
}

add_filter( 'previous_post_link', 'add_rr_linktitle', 9, 2 );
add_filter( 'next_post_link', 'add_rr_linktitle', 9, 1 );