Build process should check build requirements

ol3 has [a lot of build requirements](https://github.com/openlayers/ol3/issues/318#issuecomment-14633488). When these are not present, the build fails in [strange](https://gist.github.com/tmcw/5113095) [ways](https://gist.github.com/tmcw/ef9cfa30c2f047bfe845).

The build process should give meaningful messages when these requirements are not met. This includes, for each requirement:

 * checking that the requirement is present
 * checking that the requirement is a supported version

Refs #318.