vendor/less: upgrade from 551 to 608

vendor/less: upgrade from 551 to 608

 - Update Unicode tables.
 - Fix memory corruption when built with libtermcap.
 - Support libtinfow.
 - Fix crash on some systems due to realpath incompatibility.
 - Add the --incsearch option.
 - Add the --line-num-width option.
 - Add the --status-col-width option.
 - Add the --use-color and --color options.
 - Add the --lesskey-src option.
 - Add the --file-size option.
 - Add the --header option.
 - Add the --no-number-headers option.
 - Add the --status-line option.
 - Add the --redraw-on-quit option.
 - Add the --search-options option.
 - Add the --exit-follow-on-close option.
 - Fix bug which caused failure to respond to window resize.

For details see:
http://www.greenwoodsoftware.com/less/news.557.html
http://www.greenwoodsoftware.com/less/news.561.html
http://www.greenwoodsoftware.com/less/news.563.html
http://www.greenwoodsoftware.com/less/news.580.html
http://www.greenwoodsoftware.com/less/news.581.html
http://www.greenwoodsoftware.com/less/news.589.html
http://www.greenwoodsoftware.com/less/news.590.html
http://www.greenwoodsoftware.com/less/news.598.html
http://www.greenwoodsoftware.com/less/news.600.html
http://www.greenwoodsoftware.com/less/news.603.html
http://www.greenwoodsoftware.com/less/news.608.html