Merged upstream Ruby 2.1.7

Include upstream 2.1.6 changes

Updated with upstream 2.1.5

Updated with the upstream 2.1.4 changes.

Based off upstream 2.1.3 plus some small StringIO fixes.

Based off upstream 2.1.2 plus some additional memory usage optimization fixes.

Includes all fixes from upstream from 2.1.1 plus the fix for https://www.ruby-lang.org/en/news/2014/03/10/regression-of-hash-reject-in-ruby-2-1-1/

Based of upstream 2.1.0 including some critical fixes described here:

https://gist.github.com/tmm1/8393897

• Backport frozen string syntax from trunk

• Add method visibility predicate methods (Method#private?, #public?, #protected?) to keep Rails 2.3 working when respond_to? started ignoring protected methods in Ruby 2.0.0
• Add Encoding.compatibility? which returns true if encoding compatibility mode is on (set by --encoding-compatibility)
• Add GC stats patch
• Add encoding compatibility patch