Specs for Range#last with argument.
Style improvements for Range#first specs.
Add spec for File.basename and File.extname

Verifies the behavior when filenames have names with multibyte
characters.
Add specs for writing StringIO with binary strings
Add failing specs for issue #2215
Failing spec for __method__ in class body
Add File.realpath spec for reading relative symlinks.
Add spec for encoded string and partial match

Extracted from #2253
Add failing spec in -X19 and -X20 for shadowing pattern arguments
Add spec for treating Time marshal data as binary
Add RubySpec for Kernel#sprintf and the "%d" format
Fix race condition in Thread spec
Add spec for String#insert and multibyte strings
Add spec for IO.readlines with implicit separator and options Hash
Add spec for `MatchData#values_at` with a range arguments
Add specs for accessors on immediates
Add specs for Hash#select
Add specs for Hash#select!
Add a language spec for not expanding arrays after a splat
Add spec for StringIO#getc with multibyte strings.