Older installers, like the one on http://win.meteor.com
populated the same directory as our new installer, but with
different files. Specifically, meteor.exe which runs before
our meteor.bat. So we delete the contents of the installed
directory before starting the install.
* Always install the the user's local directory
(skip the dialog asking where to install)
* Skip login/register dialog (it doesn't work yet)
* Improve prose
