Fix `MatchData#values_at` method for a range arguments

Before:
    /(.)(\d+).(\d+)/.match("$10.99").values_at(1..3)
    # => [["$", "10", "99"]]
After:
    /(.)(\d+).(\d+)/.match("$10.99").values_at(1..3)
    # => ["$", "10", "99"]
Add spec for `MatchData#values_at` with a range arguments
Merge pull request #2275 from lexmag/fix-matchdata

Fix `MatchData#values_at` method for a range arguments
Use correct conditional because 2.0 mode behaves like 1.9
Update socket for 2.0 mode and update tags
Add specs for accessors on immediates
Fix using an accessor on immediates

Also cleans up unused code because it was inlined into Object.

Fixes #2276
Remove tags for passing specs

Also adds 2.0 mode for rbconfig specs.