vimrc: Tweaks for improved performance.
ackrc: Add .gemspec, Assetfile, Gemfile, and Rakefile as ruby.
gitignore: Ignore .ruby-gemset.
gitignore: Ignore node_modules.
gitignore: Ignore cached libv8 gems.

This library is huge and it's platform-specific anyway, so there's not
much benefit to packaging it.
gitignore: Ignore *.dump files.