Use /cygdrive when rsyncing on windows
All drive letters when using /cygdrive

Previously the code rewriting windows drive letters to /cygdrive/<letter> was hard coded to C. Now it supports all letters.
Merge pull request #17 from mbarton/master

Use /cygdrive when rsyncing on Windows
Merge branch 'master' of github.com:mitchellh/vagrant-rackspace