Permanently setting $VERBOSE to nil causes unwanted side effects (warnings generated by app code are
silenced when triggered by a rake task but visible otherwise). silence_warnings {} would be safer to
use here since it resets $VERBOSE back to what it was when the block finishes.
This makes "sprockets/railtie" explicit. This means that sprockets will
be loaded when you require "rails/all". If you are not using requiring
"rails/all", you need to manually load it with all other framework
railties.
In order to be complete, this commit also adds --skip-sprockets to
the rails generator.
