* upstream/master: (60 commits)
adds trailing +s to the output of EXPLAIN for MySQL
revises EXPLAIN tests for SQLite3
Remove redundant blank line at the bottom
Removed argument throwing warnings when running tests.
Merge pull request #3521 from nulogy/fix_postgres_adapter_to_handle_spaces_between_schemas
Added the test case for #3537
RUBY_ENGINE is not defined on 1.8
Implement a workaround for a bug in ruby-1.9.3p0.
Revert "Skip test_default_external_works on the CI for Ruby 1.9.3."
Refactored pluralize and singularize into a common method.
Docs cosmetic fixes in Action View form_helper.rb
Update ActiveRecord#attribute_present? to work as documented
Add arel to Gemfile on apps generated in edge Rails
bumps up sprockets
implements AS::Notifications.subscribed, which provides subscriptions to events while a block runs
expands the documentation of AS::Notifications
Revert "Merge pull request #2378 from cesario/remove_warnings_activemodel"