Please update dev-ruby/rest-client to ruby 1.9. I manually added "ruby19" to USE_RUBY for rest-client-1.6.7 and it built/ran fine for me. Reproducible: Always
I'm getting test failures with ruby19 so I can't add ruby19 until those are resolved.
*rest-client-1.6.7-r1 (11 Aug 2012) 11 Aug 2012; Benedikt Böhm <hollow@gentoo.org> +rest-client-1.6.7-r1.ebuild, +files/rest-client-1.6.7-ruby19.patch: add ruby19 support Tests work for me with ruby19