v0.5.1: Fix 0.6 ccall on OS X and add OS X to Travis (#131)
* Fix 0.6 ccall on OS X and add OS X to Travis * Remove unnecessary at-compat * Don't use xvfb on Mac
* Fix 0.6 ccall on OS X and add OS X to Travis * Remove unnecessary at-compat * Don't use xvfb on Mac