You can hook into the media_send_to_editor
filter and add the title tag to the generated HTML image tag:
function wpse_78529_restore_image_title( $html, $id ) {
/* retrieve the post object */
$attachment = get_post( $id );
/* if the title attribute is already present, bail early */
if ( strpos( $html, 'title=" ) )
return $html;
/* retrieve the attached image attrbute */
$image_title = esc_attr( $attachment->post_title );
/* apply the title attribute to the image tag */
return str_replace( "<img', '<img title="' . $image_title . '" ', $html );
}
add_filter( 'media_send_to_editor', 'wpse_78529_restore_image_title', 15, 2 );