Fix for AMD specs loaded after Jasmine runs

With the current version of RequireJS ATM, 2.1.1, the AMD modules containing the specs were loaded after the call to execJasmine in jasmine.helper.js, preventing any spec to be run.

The issue was that execJasmine was in the window.load callback, where it should be in the require callback when AMD is enabled.

The fix is somewhat hacky but works with my AMD environment, while preserving non-AMD behaviour.