Replace HOME/HOMEDRIVE/HOMEPATH with USERPROFILE

This isn't ready, it folds in CB-5433 (which is fairly critical) with CB-5434 (which is just improving error paths).

I'd like to standardize on USERPROFILE instead of this mess...  - That also means rewriting 5433.

This blog:
http://blogs.msdn.com/b/patricka/archive/2010/03/18/where-should-i-store-my-data-and-configuration-files-if-i-target-multiple-os-versions.aspx
talks about the correct way to find stuff, note that it's always %USERPROFILE% and never %HOMEDRIVE%/%HOMEPATH% -- that's been obsolete for a really long time, but I was in a hurry when I wrote the first patch for 5433 (and it's still better than nothing).