Don't swallow exceptions in transctional statements

The MySQL connection adapater swallows all StandardError exceptions,
which includes Mysql::Error and Mysql2::Error. The comment in the
exception clause claims errors thrown here indicate that transactions
aren't supported by the server but that isn't necessarily true. It's
possible the MySQL server has gone away and swallowing a failed commit
may let the application return a successful response when the data has
not been saved. Also, replication libraries like Galera require that the
application handle exceptions thrown at BEGIN/COMMIT.

I'm unable to determine what version of MySQL threw an exception for
transactional statements. I tried as far back as 3.23.49 with InnoDB
disabled but BEGIN & COMMIT statements do not throw an error. If there's
a real case for this logic to continue, we could instead push this
behavior into a configuration setting.

The exception swallowing has been there since the beginning:
db045dbbf60b53dbe013ef25554fd013baf88134
Also dup `column_types` in AR::Result `initialize_copy`
Refer to Rails.env only when Rails is defined
Explicitly exit with status "1" for create and drop failures

* A non-zero exit status allows subsequent shell commands to be chained
  together such as: `rake db:reset test:prepare && rspec && cap deploy`
  (if you're feeling brave :)
* Any exceptions raised during the `create` and `drop` tasks are caught
  in order to print a "pretty" message to the user. Unfortunately doing
  so prevents rake from aborting with a non-zero exit status to the shell.
* Therefore we re-raise the exceptions after the "pretty" message and
  re-catch them in the task.
* From the task we explicitly exit with a non-zero status. This method
  was chosen (rather than just letting rake fail from the exception) so
  that the backtrace is suppressed and the output to stderr is
  unchanged.
* Update activerecord CHANGELOG
Move `SchemaCreation` to its own file instead of `AbstractAdapter`.
add #no_touching on ActiveRecord models
move Relation#merge tests into separate file.
tests for merging Relations of different classes.
fix weird Emacs auto indentation. [ci skip]
Merge pull request #12772 from dmathieu/no_touching

Add No Touching
Make it clear that require 'active_support' is required [ci-skip]
Merge pull request #12874 from chancancode/better_as_loading_guides

Make it clear that require 'active_support' is required [ci-skip]
Use rescue with a splat rather and catching all and filtering
Merge pull request #12882 from charliesome/use-rescue-splat-in-suppress

Use rescue with a splat rather and catching all exceptions and manually filtering in Kernel#suppress
Updated guides link for 3.2.x to latest stable version 3.2.15 [skip-ci]
Get rid of unused  variable
Merge pull request #12883 from Amit-Thawait/master

Updated guides link for 3.2.x to latest stable version 3.2.15 [ci skip]
Merge pull request #12845 from amatsuda/should_ar_depend_on_rails

Refer to Rails.env from AR only when Rails is defined
Ruby's new Hash syntax applied in actionmailer
Merge pull request #12884 from akshay-vishnoi/refactor

Ruby's new Hash syntax applied in actionmailer