speed up acceptance tests

bundle update is notoriously slow - skip running it if we don't need to
Merge pull request #331 from ccutrer/bundle_update

speed up acceptance tests
update binstub to find spring as a subdependency

if you only add say spring-commands-rspec to your Gemfile, that will
automatically pull in the latest version of spring, but as a
sub-dependency, so there will be an extra line of indentation in the
lockfile
Merge pull request #335 from ccutrer/binstub_subdependency

update binstub to find spring as a subdependency
fix preloading of app with hidden pty with lots of output

if we never read from the PTY, and the app spews a lot of messages
on startup, it might hang because the buffer is full
fix gems that only add rake tasks

if a gem is in the rake_tasks group, it is supposed to required for
`rake`. Unfortunately, this wasn't working correctly because with
spring the app had already been initialized and had cached all
railties, so the Rakefile require rake_tasks loaded the gems,
but loading of the actual rake tasks couldn't find the railties.

This commit adds a hook for commands to preload things after
config/application has been required (and the main part of
the bundle required), but before the application actually
initializes. Rake command takes advantage of this require the
rake_tasks group