Refactoring Sandboxing to be in RSpec support

rspec-core changes for https://github.com/rspec/rspec-core/issues/1798

rspec-support changes in https://github.com/rspec/rspec-support/pull/137
On 1.8.7 (which is the context for which this fixture is used to match), these three lines don't have the `:in block...` bit.  That's what's causing the failures on travis.