Fix time_zone_options_for_select to not mutate TimeZones array

Previous implementation of time_zone_options_for_select did not dup the
ActiveSupport::TimeZone.all array.  When :priority_zones were provided
the method would reject! the zones from the memoized TimeZones array
thus affecting future requests to the server.  Essentially whatever
zones were specified as :priority_zones would show up for the first
request but then disappear from the time zone options on future
requests.
Improve upgrading guide with ActionDispatch::BestStandardsSupport removal
Merge pull request #9331 from robertomiranda/upgrading-guide

Improve upgrading guide with ActionDispatch::BestStandardsSupport remova...
Merge pull request #9330 from bdmac/time_zone_select_dup

Fix time_zone_options_for_select to not mutate TimeZones array
descriptive error message when AR adapter was not found. Closes #7313.
Merge pull request #8060 from senny/7313_descriptive_error_message_for_missing_adapter

descriptive error message when AR adapter was not found. Closes #7313
Whitespace :heart: and hash syntax change
Remove XML Parser from ActionDispatch

If you want an ability to parse XML parameters, please install
`actionpack-xml_parser` gem.
Merge pull request #9328 from sikachu/ps-remove-xml-parser

Remove XML Parser from ActionDispatch
standardize database_configuration to a hash

make connection_url_to_hash a class method

This als prevents loading database.yml if it doesn't exist
but DATABASE_URL does
test DATABASE_URL without database.yml around
run the load_structure test in the test environment
update changelog
move config.assets.precompile into config/application.rb
Merge pull request #9120 from hone/db_migrate_with_database_url

fix rake db:migrate when used with ENV['DATABASE_URL']
Reduced memory leak problem in transactions by lazily updating AR objects with new transaction state. If AR object has a callback, the callback will be performed immediately (non-lazily) so the transaction still has to keep records with callbacks.
Added comments about the check_empty_arguments method which is called
for query methods in a where_clause. Also, modified the CHANGELOG entry
because it had false information and added tests.
Merge pull request #9341 from senny/move_precompiled_asset_config_to_application

move config.assets.precompile into config/application.rb
Merge pull request #9068 from wangjohn/transaction_callback_patch

Reduced memory leak problem in transactions by lazily updating AR objects
make type_cast_value a class level method