RUBY-1211 Add Keep-Alive to Mongo::Socket::TCP.
RUBY-1211 Add Keep-Alive to Mongo::Socket::TCP.

kay-kim/mongo-ruby-driver,saghm/mongo-ruby-driver,mongodb/mongo-ruby-driver,mongodb/mongo-ruby-driver,mongodb/mongo-ruby-driver,jonhyman/mongo-ruby-driver,jonhyman/mongo-ruby-driver,kay-kim/mongo-ruby-driver,saghm/mongo-ruby-driver