Document Rails::Generators::MailerGenerator
Merge pull request #10626 from firedev/master

Removed incorrect warning from application.js templates and replaced it with stub command description
change to destructive `deep_symbolize_keys` after https://github.com/rails/rails/commit/df24b8790f22384a068fece7042f04ffd2fcb33e which allows to do so. This helps to avoid extra hash object creation, by symbolizing inplace
Added documentation for ActiveRecord::Associations::Builder::Association class
Fixes bug 10628.
Added some more documentation for ActiveRecord::Associations::Builder::Association class
Added some more documentation for define_readers and define_writer of the Association and its inherited classes
restore ability to return nil from asset_host proc, add test
Rewrite `activerecord/RUNNING_UNIT_TESTS`

`RUNNING_UNIT_TESTS` is written in an unclear and confusing manner. This commit
attempts to correct that.

Thanks to zzak and vipulnsward for feedback.
Fix HWIA#to_hash behavior with array of hashes.
Merge pull request #10601 from Ichimonji10/fix-docs

Rewrite  `activerecord/RUNNING_UNIT_TESTS.rdoc`
Merge pull request #10631 from kennyj/improve_10266

Fix HWIA#to_hash behavior with array of hashes.
use unless instead of if!
simplify the condions lambda generation
conditions are guaranteed to be arrays by initialize
stop keeping a reference to the options hash
remove deprecation notices
remove dead code
this variable is used, so we don't have to use double assignments
just call the class method since we know the callbacks are stored at the
class level