Clean up session configuration doc block
Remove extra doc line
Delete AppShell.php

The AppShell class isn't thought to be overly useful. If it is required, it can be easily resurected by users.
Use --prefer-dist option when creating project.

Since we use "-s dev" option, composer clones all dependencies making
the setup process quite slow and causes timeouts for many users.
Merge pull request #105 from cakephp/composer

Use --prefer-dist option when creating project.
Remove AppHelper as core helpers no longer extend it.