* ext/readline/readline.c (Init_readline): added
  Readline.delete_text. [ruby-dev:45789] [Feature #6626]
* ext/readline/extconf.rb: check for rl_delete_text() in Readline library.

  Thanks, Nobuyoshi Nakada, for the patch.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42101 b2dd03c8-39d4-4d8f-98ff-823fe69b080e