RUBY-545 fix for KillCursors routing
RUBY-545 only checkin socket if it was not provided
RUBY-548 As an engineer, I want to improve code coverage
SimpleCov must load before our code - and when properly configured, a coverage report summary line will print after each test suite run
gem 'test-unit' is explicitly needed in test_helper.rb for Test::Unit::TestCase.shutdown
Test::Unit::TestCase.shutdown is run to clean up after an individual test
Test::Unit::TestCase.shutdown is run once for replica set via mock test suite
rake tasks should be executed (not invoked) because we want to re-execute them, once for with-ext
 (test:ext) and once without-ext (test:ruby)
Initial coverage is 79.78%
RUBY-550 adding test to reproduce timeout socket mangling