Fixed Symbol#to_proc specs for 1.8 behavior.
Add a spec for method equality with define_method
Add spec for respond_to? and invalid argument
Fix spec descriptions for 2.0 mode
Add spec for fallback with KCODE set
Add specs for rb_sprintf with a long argument

Adds a spec where the argument to fill in is larger than the string,
probably triggering a resize in the implementation.
Add specs for File.realpath with invalid inputs
Improve spec descriptions.
Add specs for Regexp#match and String#match
Add specs for multibyte strings and String#(tr|tr_s)