Adds --force-[no-]bootstrap rule for "ript rules generate".

Fixes #9 by moving the root-only restriction into the actions that need it.

Tested with `rake features` running inside an Ubuntu 12.04 VM; until https://github.com/travis-ci/travis-ci/issues/1341 is fixed it looks like a Travis build won't be possible.

(I have [another branch](https://github.com/damncabbage/ript/compare/bulletproofnetworks:master...damncabbage:globals) that starts to move chunks of `bin/ript` out to `lib/ript/iptables.rb` and `lib/ript/cli.rb`, but this is a minimal change to get #9 in without rearranging everything; refactoring can follow if necessary.)