Code cleanup for ActionDispatch::Flash#call

The nested `if` was replaced by using `presence` which takes account for
the given hash when it is `nil` or when it is empty. The `else` was
removed because what it was doing was to assign to `env[KEY]` the
value it already had.
Merge pull request #10580 from CodeTag/master

Code cleanup for ActionDispatch::Flash#call
better error message when app name is not passed in `rails new`

Prior to this change, for the following command:

    $ rails new

we received "Options should be given after the application name" as an error message.

This is outdated and should be "Application name should be provided in arguments".
Merge pull request #10581 from shime/better-generator-error

better error message when app name is not passed in `rails new`
Fixes NoMethodError: `alias_method_chain` when requiring just active_support/core_ext

* Each file that uses `alias_method_chain` brings it in explicitly
Updated comment to Rails 4
Merge pull request #10586 from AJ-Acevedo/comments

Updated comment to Rails 4
Merge pull request #10584 from alindeman/range-missing-alias-attribute

Fixes NoMethodError: `alias_method_chain` when requiring just active_support/core_ext
Extract variable out of loop
Merge pull request #10587 from vipulnsward/indent_var

Extract variable out of loop