Dropped support for rails 2.x. Added support for Rails 4.

Updated to rspec 2.14.0. Updated specs to work with Rails 4. Added
Rails 4 to Travis config. Bumped version to 2.1.0
Merge remote-tracking branch 'sunspot/master'

Conflicts:
	.travis.yml
	sunspot/spec/api/session_proxy/class_sharding_session_proxy_spec.rb
	sunspot/spec/api/session_proxy/retry_5xx_session_proxy_spec.rb
	sunspot/spec/api/session_proxy/sharding_session_proxy_spec.rb
	sunspot/spec/api/session_spec.rb
	sunspot_rails/History.txt
	sunspot_rails/dev_tasks/spec.rake
	sunspot_rails/gemfiles/rails-4.0.0
	sunspot_rails/lib/sunspot/rails/adapters.rb
	sunspot_rails/lib/sunspot/rails/searchable.rb
	sunspot_rails/spec/configuration_spec.rb
	sunspot_rails/spec/model_spec.rb
	sunspot_rails/spec/rails_template/app/models/post_with_default_scope.rb
	sunspot_rails/spec/rails_template/config/routes.rb
	sunspot_rails/spec/session_spec.rb
	sunspot_rails/spec/spec_helper.rb