StandardError casts message to string in Ruby 1.9

When passing a message to StandardError in ruby 1.8, it will keep that object intact. Ruby 1.9 will convert to a String. Spent more time than I wanted to chasing this down.

In ruby 1.8.7:

>> RUBY_VERSION
=> "1.8.7"
>> err = StandardError.new(Object.new)
=> #<StandardError: #<StandardError:0x78952527>>
>> err.message.class
=> Object

In ruby 1.9.3:

>> RUBY_VERSION
=> "1.9.3"
>> err = StandardError.new(Object.new)
=> #<StandardError: #<Object:0x456c5f50>>
>> err.message.class
=> String