Fix remaining Ruby warnings.

- spec/rspec/rails/minitest_lifecycle_adapter_spec.rb:
  > warning: assigned but unused variable - example

- spec/support/shared_examples.rb
  > warning: assigned but unused variable - spec_file

Ruby 1.9.3 seems to erroneously report the following warning:

- lib/rspec/rails/matchers/have_http_status.rb:
  > warning: assigned but unused variable - _ignored

This is logged on ruby-trunk: https://bugs.ruby-lang.org/issues/9943
Update Capybara to remove matcher deprecations.
Upgrade Aruba gem dependency.

The new version requires an additional, optional, `timeout` argument.
Include this argument in the world shim.
Fix Ruby 1.8.7 warning about regex syntax.

Noticed this when running against Ruby 1.8.7, there were two repeated
warnings based on improper escaped brackets:

- spec/rspec/rails/matchers/route_to_spec.rb:114:
  > warning: regexp has invalid interval

- spec/rspec/rails/matchers/route_to_spec.rb:114:
  > warning: regexp has `}' without escape
Bump version to 3.1.0.pre to prevent confusion with master being 3.0.0 but 3.0.x releases are out.
updating feature docs to reflect 3.0 final release
Merge pull request #1092 from plentz/patch-2

updating feature docs to reflect 3.0 final release
Merge pull request #1089 from rspec/fix-ruby-warnings

Fix warnings and deprecations notices
updating feature docs to reflect capybara 2.2.0 dependency

change made in 8254ddc10c8e34912300ca2c8df275cc5132d1ba
updating to 2.3.0 which fixes some warnings
Merge pull request #1091 from plentz/patch-1

updating feature docs to reflect capybara 2.3.0 dependency
Update changelog with Capybara bump.
rolling back the capybara bump to not break SemVer. updating docs to suggest 2.3 or later. related #1091
missing space
Merge pull request #1094 from tautt/master

rolling back the capybara version bump to not break SemVer
Allow RSpec::Rails to load without rubygems
'git move' should be 'git mv'
Merge pull request #1102 from rspec/upgrade-documentation-tweak

'git move' should be 'git mv' in upgrade docs
Document Rails 4.x improvements to schema changes.
Move upgrade details into feature docs.

Duplicating the documentation in two places was causing some information
to be dropped. Additionally, the README.md file was starting to be
consumed by the upgrade notes.

- Use the feature documentation as the primary location for the upgrade
  docs.
- List the important topics users need to be aware of in the README and
  link them to the section of the upgrade guide