Fixed display of breadcrumb images in GC Web Usability theme.
Added fallback background colour for GC Web Usability intranet banner (to avoid white text on a white background).
Use sequential gem install

For issue with Travis
Merge pull request #946 from nschonni/sequential-gem-install-940

Use sequential gem install
Don't run post build during PR testing

Check Travis's env variable TRAVIS_PULL_REQUEST to see if the post build
should be run at all
Use public Travis build number in commit message

I previously set the job ID instead of the build number as described in
the documents
http://about.travis-ci.org/docs/user/ci-environment/#Environment-variables