Various changes for Travis

Hi Zeno

The last commit made everything pass (Ruby 1.9.2, 1.9.3 and 2.0.0) 
see https://travis-ci.org/ngiger/htmlgrid/builds/9903807

Changes for the developer are that he should just call rake to run all unit-tests.

You could even set up your travis-di.org or github.com/zdavatz to see whether all proposed push request are 'green'.

Regards