Redgate's solution seems to be for versioning your database, not your files in your Solution Explorer. I've found two options for solution versioning:
1) Setting up TortoiseSVN as an external tool: http://jrummell.com/sql-server-management-studio-and-tortoisesvn
2) Agent SVN: http://www.zeusedit.com/agent/ssms/ms_ssms.html
I've tried neither of these options yet, but perhaps this helps someone's search