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.
Stop to create directories in default gem directory for test

It breaks test on system installed RubyGems and normal user
environment with the following error:

      1) Error:
    test_generate_default_gem(TestRDocRubygemsHook):
    Errno::EACCES: Permission denied - /var/lib/gems/2.0.0/doc/a-2
        /usr/lib/ruby/2.0.0/fileutils.rb:245:in `mkdir'
        /usr/lib/ruby/2.0.0/fileutils.rb:245:in `fu_mkdir'
        /usr/lib/ruby/2.0.0/fileutils.rb:219:in `block (2 levels) in mkdir_p'
        /usr/lib/ruby/2.0.0/fileutils.rb:217:in `reverse_each'
        /usr/lib/ruby/2.0.0/fileutils.rb:217:in `block in mkdir_p'
        /usr/lib/ruby/2.0.0/fileutils.rb:203:in `each'
        /usr/lib/ruby/2.0.0/fileutils.rb:203:in `mkdir_p'
        /home/kou/work/ruby/rdoc/test/test_rdoc_rubygems_hook.rb:141:in `test_generate_default_gem'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:1301:in `run'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:919:in `block in _run_suite'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:912:in `map'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:912:in `_run_suite'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:899:in `block in _run_suites'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:899:in `map'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:899:in `_run_suites'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:867:in `_run_anything'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:1060:in `run_tests'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:1047:in `block in _run'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:1046:in `each'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:1046:in `_run'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:1035:in `run'
        /usr/lib/ruby/2.0.0/minitest/unit.rb:789:in `block in autorun'

We don't need to create directories because the test checks that
RubyGems hook isn't ran.
Merge pull request #286 from kou/fix-default-gem-test

Do not create directories in test/
Add #286 to History
Merge pull request #285 from kou/improve-auto-setup

Improve auto setup
Add #285 to History
Fix outdated documentation example for markup.rb

ToHTML.new takes two arguments, and the markup object is the second argument.
Update outdated documentation in markup.rb
Merge pull request #292 from sandal/patch-1

Fix outdated documentation example for markup.rb
Add #292 to History