Merge branch 'sg/travis-fixes'

Assorted updates for TravisCI integration.

* sg/travis-fixes:
  travis-ci: only print test failures if there are test results available
  travis-ci: save prove state for the 32 bit Linux build
  travis-ci: don't install default addon packages for the 32 bit Linux build
  travis-ci: fine tune the use of 'set -x' in 'ci/*' scripts