Fix symbolic link for Firefox addon
Fix bug that caused addons not to run

run_custom_stage only got called if the stage was specified in the
config, so if there's no `before_install` or `before_script` stage in
the config already, the addons won't run as they should.
Update Groovy example
Add hosts addon

Requested in #86.

This allows for an easy way to add a hostname to the hosts file linking
to 127.0.0.1.

Usage:

Add the following to the .travis.yml file to link foobar.local to
127.0.0.1:

addons:
  hosts:
    - foobar.local
Don't run setup addons twice

The setup stage will be run just like any other stage through the Stages
module, which will in turn call this method, causing any addons using
the setup stage to run twice.
Add IPv6 support to hosts addon

Update ::1 as well as 127.0.0.1 for the added hostname to enable both
stacks for the hostname.
Insert appropriate amount of backslashes
Update sed command line options

The version of sed on our servers doesn't like "-i ''", it thinks that
"''" is another file name and then complains it can't find a file with a
blank filename.
Add a fold around the hosts addon
Merge pull request #101 from travis-ci/hh-hosts-addon

Add hosts addon
Closes #86
Haskell: Run `cabal update` before running any other scripts (again!)
Add fold to cabal update
Remove duplicate spec
update the year and contact person/org in the LICENSE file
Update readme, mostly correcting the use of Travis Build.
Alias 'rbx' to 'rbx-weekly-d18'

This was requested in #89

From that issue:

> This is the most similar given the old defaults on Travis (ie, Rubinius
> defaults to 1.8 mode and Travis was updated every few weeks with a build
> of the Rubinius 2.0.testing branch).
Update examples