Update RubySpec from rubyspec/rubyspec @ dfb927d4.

RubySpec should be updated from canonical repo and
Rubinius' copy should be merged regularly as in
https://github.com/rubyspec/rubyspec/pull/295.

Keep the .gitignore since it correclty ignores
the automatically generated CAPI version file
spec/ruby/optional/capi/ext/rubyspec_version.h.
Update to latest mspec.
[Truffle] Tag new failing specs.
[Truffle] Implement String#sub following String#gsub.
[Truffle] Implement String#rstrip.

* For RubySpec's evaluate.
[Truffle] Implement String#each_line.
[Truffle] Implement Array#join() and add $,.
[Truffle] Fix String#{sub,gsub}(String) to escape it.

* We could also try to have a smarter string replace directly wihtout Regexp.
[Truffle] Fix String#[](int).
[Truffle] Restore method specs.
[Truffle] Fix String#[rng] and Array#[rng].

* Remove getInclusiveEnd since unused and dangerous.
* getExclusiveEnd should only ever be used on RangeNodes,
  other uses need to normalize index first before considering
  exclusion status.
[Truffle] Restore lambda specs.
Implement negation of Complex and Rational nodes.
[Truffle] Restore numbers specs.