Ruby

[ruby/irb] Refactor RubyLex's input/io methods
(https://github.com/ruby/irb/pull/583)

1. Make RubyLex#set_input simply assign the input block. This matches
   the behavior of RubyLex#set_prompt.
2. Merge RubyLex#set_input's IO configuration logic with #set_auto_indent
   into #configure_io.