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
Update security.md

Hi Guys 
I was reading through this guide last night and noticed a small mistake, would be great if you could update it. 
I changed the word 'building' to 'build' in line 20. 
"Web application frameworks are made to help developers building web applications"
Also dup `column_types` in AR::Result `initialize_copy`
Refer to Rails.env only when Rails is defined
Fixed typo in migrations guide

Product model name was pluralized in example in migrations guide.
[ci skip]
Merge pull request #12847 from jipe/master

Fixed typo in migrations guide [ci skip]
Do not count "SHOW CREATE TABLE" queries when testing against mysql
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
test cases to describe the MySQL boolean behavior.
Unifies mysql and mysql2 casting of booleans.
Merge pull request #12425 from senny/mysql_booleans

Unify boolean quoting for Mysql- and Mysql2Adapter.
Merge pull request #12815 from Adam89/patch-1

Update security.md [ci skip]
Prevent the counter cache from being decremented twice

when destroying a record on a has_many :through association.
:destroy method has own counter_cache callbacks.
documentation updated for Hashes [ci skip]
Merge pull request #12748 from dm1try/fix_counter_cache_for_through_association

Fixes #11079, prevent the counter cache from being decremented twice when destroying a record on a has_many :through association
Merge pull request #12854 from kuldeepaggarwal/f-indentation

methods and outputs indented [ci skip]
updated documentation for Integer
Allow Pathnames to be added to eager load paths
Make static error pages responsive
Merge pull request #12555 from EtienneLem/responsive-static-pages

Make static error pages responsive