`Readline::HISTORY << str` and push should return HISTORY

I've sent a pull request:
https://github.com/jruby/jruby/pull/65

For the record, I repost it here:
As other rubies:

$ ruby -vrreadline -e 'p(Readline::HISTORY<<"a")'
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10.8.0]
HISTORY

$ /usr/bin/ruby -vrreadline -e 'p(Readline::HISTORY<<"a")'
ruby 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]
HISTORY

$ rbx -vrreadline -e 'p(Readline::HISTORY<<"a")'
rubinius 1.2.4 (1.8.7 release 2011-07-05 JI) [x86_64-apple-darwin10.8.0]
HISTORY

Thanks!