Unknown commands crash interpreter

[camdez]

To reproduce:

Add a keybinding to your ~/.inputrc file which references a non-existent command.

Might I suggest the following since you need to put a literal escape character in the file for bindings to work (#105):

$ ruby -e 'puts "\"\en\": next-history"' >> ~/.inputrc

Then run rb-readline and press Meta-N:

$ ruby -Ilib -S irb                                   
irb(main):001:0> /Users/camdez/src/rb-readline/lib/rbreadline.rb:4322:in `_rl_dispatch_subseq': undefined method `rl_next_history' for RbReadline:Module (NoMethodError)
        from /Users/camdez/src/rb-readline/lib/rbreadline.rb:4331:in `_rl_dispatch_subseq'
        from /Users/camdez/src/rb-readline/lib/rbreadline.rb:4311:in `_rl_dispatch'
        from /Users/camdez/src/rb-readline/lib/rbreadline.rb:4727:in `readline_internal_charloop'
        from /Users/camdez/src/rb-readline/lib/rbreadline.rb:4801:in `readline_internal'
        from /Users/camdez/src/rb-readline/lib/rbreadline.rb:4823:in `readline'
        from /Users/camdez/src/rb-readline/lib/readline.rb:45:in `readline'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/input-method.rb:152:in `gets'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb.rb:472:in `block (2 levels) in eval_input'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb.rb:624:in `signal_status'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb.rb:471:in `block in eval_input'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:190:in `call'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:190:in `buf_input'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:105:in `getc'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/slex.rb:206:in `match_io'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/slex.rb:76:in `match'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:290:in `token'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:266:in `lex'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:237:in `block (2 levels) in each_top_level_statement'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:233:in `loop'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:233:in `block in each_top_level_statement'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:232:in `catch'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb/ruby-lex.rb:232:in `each_top_level_statement'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb.rb:488:in `eval_input'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb.rb:397:in `block in start'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb.rb:396:in `catch'
        from /usr/local/var/rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/irb.rb:396:in `start'
        from /usr/local/var/rbenv/versions/2.0.0-p247/bin/irb:12:in `<main>'

This is a big problem as some commands are named differently between GNU Readline and rb-readline (e.g. GNU Readline's next-history shown here, and rb-readline's get-next-history), and therefore a valid .inputrc file with real GNU Readline commands might crash the interpreter while a user is attempting to use an rb-readline powered tool.

I'd recommend that unknown commands be ignored as they are in GNU Readline.