Add .travis.yml file.

Only Qt 4 is available on 12.04 LTS that Travis runs. There are
PPAs with Qt 5 but they are not supported anymore. Once Travis is
on 14.04 LTS we can start testing on Qt 5 as well.
Forgot "make" command :)

*facepalm*.
Pass -spec linux-$CC to qmake.
Don't try to use clang at all.

That was probably a little too ambitious with Qt 4.
Add -qq to apt-get install command.
Merge pull request #12 from estan/add-travis-yml

Add .travis.yml file.