Made two big improvements to the Windows port, in just a few hours.
First, got gpg working, and encrypted special remotes work on Windows.
Next, fixed a permissions problem that was breaking removing files
from directory special remotes on Windows.
(Also cleaned up a lot of compiler warnings on Windows.)

I think I'm almost ready to move the Windows port from alpha to beta
status. The only really bad problem that I know of with using it is that
due to a lack of locking, it's not safe to run multiple git-annex
commands at the same time in Windows.