Enable OSX builds on Travis-CI

[kylelutz]

It looks like Travis-CI now supports building a project on both Linux and Mac OS X. We should enable this for Boost.Compute to increase the test coverage and catch OS X specific issues quickly. Some investigation may have to be done on running OpenCL effectively on Travis-CI with OS X.

See http://blog.travis-ci.com/2014-05-13-multi-os-feature-available/ for a brief overview.

[roshanrags]

I contacted Travis's support a few days back about this and am about to get it enabled in my fork...

[kylelutz]

Awesome! Thanks for working on this.

[kylelutz]

Implemented in PR #415.

[kylelutz]

Implemented in PR #554.