windows: install fixes
windows: install fixes

* set default installation drive to C:\
* remove Win64 component property

R=golang-dev, bradfitz, aram
CC=golang-dev
http://codereview.appspot.com/5901044

Committer: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang