Allow custom asset host to be passed in asset_url
Improve documentation for asset_url

Updated CHANGELOG.md with entry about :host in asset_url
Small refactoring on clear_transaction_record_state

Make sure when we clean the `@_start_transaction_state` var we do it in
the same code-path.
Also this makes `clear_transaction_record_state`, more consistent with `restore_transaction_record_state`
Clear transaction state if callback raise rollback
fixed a typo [ci skip]
Merge pull request #15133 from ShunsukeAida/master

fixed a typo
Document conflicts in `db/schema.rb` [ci skip]
Merge pull request #15113 from leafac/document-schema-conflicts

Document conflicts in `db/schema.rb` [ci skip]
Remove code related to adapter which are no longer in repo

As we have remove code for these adapters so no need to have tasks
Our test suite isn't ready to run in random order yet :cry:
Merge pull request #15021 from hubertlepicki/allow_custom_host_in_asset_url

Allow custom asset host to be passed in asset_url
Merge pull request #15131 from arunagw/aa-cleanup-rakefile

Remove code related to adapter which are no longer in repo
Merge pull request #15125 from arthurnn/small_refactoring_transaction_clear

Small refactoring on clear_transaction_record_state
Add a specific method to force the transaction record state clear

We are using that code path in only one place so we should not add a
conditional to all the other cases. This will avoid performance
regressions on the old paths.
Missed if :bomb:
Reuse the force_clear_transaction_record_state
prepend mutates the string so we can remove the assignment
Remove the assignment for real this time.

cc:
https://github.com/rails/rails/commit/a11e2fcff8cdc9691b977d8330abe63024f8c732#commitcomment-6353614
and 0369dbf
Merge pull request #15139 from zzak/habtm_build_model_name

Remove the assignment for real this time.
Remove unecessary require