multiple actions for :on option with `after_commit` and `after_rollback`

Closes #988.
Changelog improvements, use 1.9 style hash in examples [ci skip]
Move number_to_human test from AP to AS

Since all changes from #9347 are related to AS, it seems proper that the
test is placed there as well.
Fix debug helper not inspecting on Exception

The debug helper should inspect the object when it can't be converted to YAML, this behavior was changed in 8f8d8eb1465069e2ed9b6f2404aa9d02e785f534.
Merge pull request #9387 from boukevanderbijl/master

Fix debug helper not inspecting when it can't convert to YAML
forwardport #9388 rename/remove column preserves custom PK.
rename_column_test.rb -> columns_test.rb to reveal intent.

I renamed the test to better communicate it's intention. Since it also tests:
  - add_column
  - remove_column
  - change_column
There is no reason to call it rename_column_test.
Merge pull request #9389 from senny/forwardport_9388

Forwardport #9388 rename/remove column preserves custom PK.
adds a missing LIMIT 1 in #take docs
guides/rails_guides moved up and out of the railties directory
Merge pull request #9393 from rubys/master

guides/rails_guides moved up and out of the railties directory
registers the encrypted session store in the AP changelog
prevent minitest from printing a --seed run option

See the first FIXME comment in the patch for the rationale.
Revert "prevent minitest from printing a --seed run option"

Reason: on a second thought, minitest prints a seed as run option
regardless of the test order, and it actually calls srand, so
albeit it might be misleading I believe, it is the way it is and
should be left that way.

This reverts commit c15862ae0cb876d745609170f0f90a9bb9b5e0ae.
also rename the test-case class inside columns_test.rb
Merge pull request #9394 from senny/actually_rename_the_test_case

also rename the test-case class inside columns_test.rb
Oracle enhanced adapter shortens its name if it is longer than 30 bytes
because of Oracle database index length spec.
Merge pull request #9395 from yahonda/oracle_index_length

Address failure test_rename_column_with_multi_column_index with Oracle
test case to prevent duplicated associations with custom PK.

closes #9201
Merge pull request #9397 from senny/9201_duplicate_associations_with_natural_key

test case to prevent duplicated associations with custom PK.