On July 18, Travis upgraded their default build VM
to Ubuntu Trusty. Trusty has cmake 3.5.1, which allows us to
drop our bundled version.
We explicitely set "dist: trusty" to prevent our build jobs
from being routed to an older build VM.
* Update cmake
* Update cmake, make Travis use it
* Enable all tests in a single command : make check
* Make cmake flawlessly run with Debian jessie cmake 3.0.2
* Make Travis use our own cmake 3.0.2 compiled version
* Typo in preferred version
* Be sure travis will have gettext
