When the adapter is with prepared statement disabled and the binds array
is not empty the connection adapter will try to set the binds values and
will fail. Now we are checking if the adapter has the prepared statement
disabled.

Fixes #12023

This reverts commit cb1d07e4, reversing
changes made to 754a373e.

Using the mysql2 adapter, boolean values were sometimes being incorrectly cast
to 't' or 'f'. This changes the cast to match the mysql adapter behavior, ie 1 and 0.

removed two instances of add_column_options! from abstract_mysql_adapter

reworked rename_column_sql to remove add_column_options from schema_statements

changed to use new hash syntax.

enum includes text or blob or ... hooked by wrong regex

Adds support for algorithm option in MySQL indexes
Moves USING and algorithm options upstream

The syntax is still specific to the Adapter, so the actual executed string happens
in the corresponding adapter

Created a layer of abstraction for the valid type checking in schema dumper. Now, connection handles the check for valid types so that each database can handle the changes individually.

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.

This reverts commit 408227d9, reversing
changes made to dca0b57d.

We should only type cast when we need to use.

Related to 4b005fb3

When a table or a column is renamed related indexes kept their name. This will lead to confusing names. This patch renames related indexes when a column or a table is renamed. Only indexes with names generated by rails will be renamed. Indexes with custom names will not be renamed.

It was supposed to be removed by the preceding two reversions but I did
them in the wrong order.

This reverts commit 5d528f83.

Relates to f8c8ad56 which is also getting reverted due to failing test.

* Fix Migration#reversible by not using `transaction`.

* Adapt mysql adapter to updated api for remove_column

* Update test after aedcd683

in the new 'variables:' hash in each database config section in database.yml.
The key-value pairs of this hash will be sent in a 'SET key = value, ...'
query on new database connections.

The configure_connection methods from mysql and mysql2 into are
consolidated into the abstract_mysql base class.

In non-strict mode it is '', but if someone is in strict mode then we
should honour the strict semantics.

Also, this removes the need for a completely horrible hack in dirty.rb.

Closes #7780

This reverts commit abf8de85.
We should take a deeper look to those cases flat_map doesn't do deep
flattening.

irb(main):002:0> [[[1,3], [1,2]]].map{|i| i}.flatten
=> [1, 3, 1, 2]
irb(main):003:0> [[[1,3], [1,2]]].flat_map{|i| i}
=> [[1, 3], [1, 2]]

When inserting new records, only the fields which have been changed
from the defaults will actually be included in the INSERT statement.
The other fields will be populated by the database.

This is more efficient, and also means that it will be safe to
remove database columns without getting subsequent errors in running
app processes (so long as the code in those processes doesn't
contain any references to the removed column).

If your database supports setting the isolation level for a transaction,
you can set it like so:

  Post.transaction(isolation: :serializable) do
    # ...
  end

Valid isolation levels are:

* `:read_uncommitted`
* `:read_committed`
* `:repeatable_read`
* `:serializable`

You should consult the documentation for your database to understand the
semantics of these different levels:

* http://www.postgresql.org/docs/9.1/static/transaction-iso.html
* https://dev.mysql.com/doc/refman/5.0/en/set-transaction.html

An `ActiveRecord::TransactionIsolationError` will be raised if:

* The adapter does not support setting the isolation level
* You are joining an existing open transaction
* You are creating a nested (savepoint) transaction

The mysql, mysql2 and postgresql adapters support setting the
transaction isolation level. However, support is disabled for mysql
versions below 5, because they are affected by a bug
(http://bugs.mysql.com/bug.php?id=39170) which means the isolation level
gets persisted outside the transaction.

Conflicts:
	activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb