Drop Ruby < 2.3 support

[pirj]

Better viewed ignoring indentation changes https://github.com/rspec/rspec-mocks/pull/1349/files?diff=split&w=1

Sibling PRs:

• Drop Ruby < 2.3 support rspec-support#436
• Drop Ruby < 2.3 support rspec-expectations#1231
• Drop Ruby < 2.3 support rspec-core#2787

As per rspec/rspec#61 (comment)

• Is this needed in spec_helper.rb
  config.extend RSpec::Support::RubyFeatures
  config.include RSpec::Support::RubyFeatures
• RSpec::Support.require_rspec_support 'ruby_features'
• Usage of RubyFeatures
• clean predicate_functions
• [-] check respond_to?
• check method_defined?
• check send (where we call private methods that later became public)
• check if we require_rspec_support ruby_features where RubyFeatures are not used
• check define_method where def would suffice
• check 1.8, 1.9, 2.0, 2.1, jruby, 9.0, 9.1, mri
• check eval
• clean up if RUBY_VERSION < "2.3" || backed_up_method_owner[method_name.to_sym] == self
• change old ruby induced rubocop settings, fix offences
• [#] Private method error changes when method_missing is defined but should not jruby/jruby#1398 - only fixed in JRuby 9.2
• Can work without this check? Gemfile|28| 4:if RUBY_VERSION <= '2.3.0' && !!(RbConfig::CONFIG['host_os'] =~ /cygwin|mswin|mingw|bccwin|wince|emx/)
• skip "This intermittently fails on JRuby" if RUBY_PLATFORM == 'java'
• remove handle_restoration_failures?
• remove expect_output_warning_on_ruby_lt_2
• check "jruby"
• clean? return Object unless Object.ancestors.last == ::BasicObject
• clean if defined?(BasicObject)

[benoittgt]

Ouhaoo. So happy with those changes. I have few questions.

[pirj]

Update: reverted the removal of rescue NameError from lib/rspec/mocks/method_double.rb.

[pirj]

I'm combining ReentrantMutex and Mutex in rspec-support, so going to change those two require statements:

rspec-mocks/lib/rspec/mocks/message_expectation.rb:RSpec::Support.require_rspec_support 'mutex'
rspec-mocks/lib/rspec/mocks/proxy.rb:RSpec::Support.require_rspec_support "mutex"