Support enforceDefine to detect IE 6 - 8 script.onerror issues.

[kr1zmo]

Dojo uses a very similar appeal to requirejs; Here is the documentation on how requirejs fixed this issue. ​http://requirejs.org/docs/api.html#ieloadfail

It gets around this persistant issue by adding the enforceDefine property on the configuration object. When enforceDefine: true all modules loaded must call define(); requirejs uses that define call to fire an event and determine if the script was loaded. I highly suggest supporting this feature as IE cannot determine if a script was loaded when the response header wasn't 200.

[bill]

Duplicate of #16416.