dev-ruby/rexical-1.0.5-r1: Support ruby20.
dev-ruby/rake-compiler-0.8.3: Support ruby20. WIP, tests should be fixed after rspec bump.
dev-ruby/nokogiri-1.5.10: Bump and Support ruby20.
Some tests are failed with >=libxml2-2.9.0.
https://github.com/sparklemotion/nokogiri/issues/829