Win0.5.7

Hi Tom,

I've done some work getting the 0.5.7 branch working on windows, and have prepared some changes as per this pull request. (branch win0.5.7).

The merge was pretty simple, but I may have done it the wrong way around - I took meteor/meteor master and applied your changes. Then applied some minor changes on top.

Other things to note are that for me Git bash didn't have mktemp and it was easy enough to work around that.

I also wasn't sure where to stash the built msi (you seem to have been using dropbox), but I wasn't sure whether to just submit to the repo.

Regards,
  Stephen

PS I already signed the meteor contributors app.