Configure standalone travis build for kohana/core

Adds and configures kohana/koharness to build a skeleton Kohana
application and then uses that environment to run the unit tests
on travis (and locally, if required).
Remove physical path dependency in Kohana::module tests

Backports dd926956 to 3.3 - MODPATH is unreliable in a koharness
environment as it will usually be a symlink. With this change the test
of Kohana::modules will pass wherever the code happens to be
deployed on the disk. This will conflict when we merge up to 3.4
because that commit uses short array syntax which is not available
in the 3.3 series.