Ruby 1.9 Compat: Redefining object_id and Rational.new!

This patch fixes two Ruby 1.9 compatibility issues:

• Use of Rational.new! in the active_support tzinfo classes, which is a private method in Ruby 1.9
• Inadvertent redefining of object_id in active_record, which yields a scary "This may cause serious issues" in Ruby 1.9

Thanks,

Nate