Upgrade bundled readline to version 5.0.

cmd-line-utils/readline/INSTALL:
  Import readline-5.0
cmd-line-utils/readline/Makefile.am:
  Import readline-5.0
cmd-line-utils/readline/README:
  Import readline-5.0
cmd-line-utils/readline/bind.c:
  Import readline-5.0
cmd-line-utils/readline/callback.c:
  Import readline-5.0
cmd-line-utils/readline/chardefs.h:
  Import readline-5.0
cmd-line-utils/readline/complete.c:
  Import readline-5.0
cmd-line-utils/readline/configure.in:
  Import readline-5.0
cmd-line-utils/readline/display.c:
  Import readline-5.0
cmd-line-utils/readline/funmap.c:
  Import readline-5.0
cmd-line-utils/readline/histexpand.c:
  Import readline-5.0
cmd-line-utils/readline/histfile.c:
  Import readline-5.0
cmd-line-utils/readline/history.c:
  Import readline-5.0
cmd-line-utils/readline/history.h:
  Import readline-5.0
cmd-line-utils/readline/histsearch.c:
  Import readline-5.0
cmd-line-utils/readline/input.c:
  Import readline-5.0
cmd-line-utils/readline/isearch.c:
  Import readline-5.0
cmd-line-utils/readline/keymaps.c:
  Import readline-5.0
cmd-line-utils/readline/kill.c:
  Import readline-5.0
cmd-line-utils/readline/macro.c:
  Import readline-5.0
cmd-line-utils/readline/mbutil.c:
  Import readline-5.0
cmd-line-utils/readline/misc.c:
  Import readline-5.0
cmd-line-utils/readline/nls.c:
  Import readline-5.0
cmd-line-utils/readline/parens.c:
  Import readline-5.0
cmd-line-utils/readline/posixdir.h:
  Import readline-5.0
cmd-line-utils/readline/readline.c:
  Import readline-5.0
cmd-line-utils/readline/readline.h:
  Import readline-5.0
cmd-line-utils/readline/rldefs.h:
  Import readline-5.0
cmd-line-utils/readline/rlmbutil.h:
  Import readline-5.0
cmd-line-utils/readline/rlprivate.h:
  Import readline-5.0
cmd-line-utils/readline/rlstdc.h:
  Import readline-5.0
cmd-line-utils/readline/rltty.c:
  Import readline-5.0
cmd-line-utils/readline/rltty.h:
  Import readline-5.0
cmd-line-utils/readline/rltypedefs.h:
  Import readline-5.0
cmd-line-utils/readline/search.c:
  Import readline-5.0
cmd-line-utils/readline/shell.c:
  Import readline-5.0
cmd-line-utils/readline/signals.c:
  Import readline-5.0
cmd-line-utils/readline/terminal.c:
  Import readline-5.0
cmd-line-utils/readline/text.c:
  Import readline-5.0
cmd-line-utils/readline/tilde.c:
  Import readline-5.0
cmd-line-utils/readline/undo.c:
  Import readline-5.0
cmd-line-utils/readline/util.c:
  Import readline-5.0
cmd-line-utils/readline/vi_mode.c:
  Import readline-5.0
cmd-line-utils/readline/xmalloc.c:
  Import readline-5.0