Check for proj4 in a way that also works in module environments

[ahocevar]

This is better than #2330, and it should also address @probins's concern.

[marcjansen]

Please merge once travis is happy, Andreas. Thanks.

[mokkabonna]

This still requires proj4 to be in the global namespace even when using module loaders. And since proj4 hides from the scope when using AMD this requires code that uses it to force a leak of proj4 like this: window.proj4 = proj4

Something like this needs to be done:

(function (root, factory) {
  if (typeof define === "function" && define.amd) {
    define(['proj4'], factory);
  } else if (typeof exports === "object") {
    //is this for node??, if so use this, if not root.proj4 as well here
    module.exports = factory(require("proj4"));
  } else {
    root.ol = factory(root.proj4);
  }
}(this, function (proj4) {

[ahocevar]

@mokkabonna Thanks for pointing this out. Would you be able to provide a pull request with this fix?

[tcoopman]

@mokkabonna I would love a fix for this!

[mokkabonna]

I can put together something yes. Just need to find some time, will put it in my backlog :)