Improve racc gem requirement check

We need racc gem when any generated file by racc doesn't exist or any
generated file by racc is older than racc source file.
Ensure installing rack for auto "rake newb" mode

We need to run "rake check_extra_deps" before "rake newb" because we
can't find racc gem installed by "rake newb" in the same process.
Merge pull request #285 from kou/improve-auto-setup

Improve auto setup