Actually it's more difficult than I thought because I thought this PR had been accepted https://github.com/theintern/intern/pull/137 which it hasn't
It's not currently possible to access args in this way (accessing within the dojo intern runtime e.g. `if (process.argv["IE"]) {intern.environments = ......}`  and it's certainly not possible in a grunt task because the arguments are rebuilt and passed to a new spawned process.

I think the options are:
*  create a new intern config (for windows people) - seems unnecessary and overkill e.g. what about linux users who don't have safari?
*  add IE to the current local environments and comment out if necessary. I prefer this, I do it all the time when developing tests as I don't want to run all browsers