transactional migration test-case was broken.

The cleanup commit a85625d broke the test-case.
The schema was no longer modified so there was no
way to check that the rollback actually happened.
transactions can be turned off per Migration.

Closes #9483.

There are SQL Queries that can't run inside a transaction. Since
the Migrator used to wrap all Migrations inside a transaction there
was no way to run these queries within a migration.

This patch adds `self.disable_ddl_transaction!` to the migration to
turn transactions off when necessary.
Typo in comment to ActionView::Resolver#find_all
Merge pull request #9585 from RKushnir/patch-1

Typo in comment to ActionView::Resolver#find_all
Merge pull request #9507 from senny/9483_migrations_without_transactions

Transactions can be turned off per Migration
`Connection#structure_dump` is no longer used. #9518

As of ccc6910c we use `mysqldump` to create the `structure.sql`.
The old `#structure_dump` code is still in AR but never used.

I removed all relevant parts from the code-base.
rake db:structure:dump warns when `mysqldump` is not in PATH.

Closes #9518.

The rake task used to fail silently and left an empty `structure.sql`.
It's confusing for users to get to the root of the problem.
The warning message tells them where to look.
Merge pull request #9538 from senny/remove_structure_dump

`Connection#structure_dump` is no longer used