Remove the usage of APC and try to build on PHP-5.5
Remove 5.5, and skip installing packages using apt-get as most of them seem to be already installed
Use the Memcached adapter instead of the APC one for the Behat test suite
Enable 5.5 again
Merge pull request #200 from christeredvartsen/travis-ci-php-5.5

Remove the usage of APC and try to build on PHP-5.5