Add .ruby-version to 1.9.3

We don't actually execute any Ruby in this project, except for during
the build process.

I think this will alleviate some issues when installing gems:

    sudo: no tty present and no askpass program specified
    Sorry, try again.

    Gem::Exception: Cannot load gem at [/var/lib/gems/1.9.1/cache/sass-3.2.12.gem]
Use bundle exec when building Sass in production

So that we use the copy of the sass binary in vendor/cache.
Fix neg number bug in roundToSignificantFigures

And make it a method on View.
Move rounding changes tests into correct place

And remove one duplicate.

And tidy whitespace on an object, remove unused thresholds (they're
duplicated below).
Change rounding thresholds from 500 to 1000

For all orders of magnitude.

I think there's an opportunity for some refactoring here.
Merge pull request #119 from alphagov/54184200-change-rounding-thresholds

Change rounding thresholds
Merge pull request #112 from alphagov/add-ruby-version

Add .ruby-version to 1.9.3
Merge branch 'master' into add-currency-symbols-clean-branch

Conflicts:
	spec/shared/extensions/views/spec.view.js