even if readline() interrupted.
* ext/readline/readline.c: returned string need to
be tainted.
* ext/readline/readline.c: fixed memory leak.
* ext/readline/readline.c: allow negative index.
* ext/readline/readline.c: added Readline::HISTORY.size
same as Readline::HISTORY.length
* ext/readline/readline.c: allow conditional parsing
of the ~/.inputrc file by `$if Ruby'.
* ext/readline/extconf.rb: check whether the
libreadline has the variable `rl_completion_append_character'
(this feature was implemented from GNU readline 2.1).
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@1735 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
