windows permissions fix

windows permissions fix

Windows: Fix permission denied error when dropping files that have the
readonly attribute set.

Files coming from a special remote may have had write permission removed
from them. The directory special remote does that. And there are
probably others. So rather than fixing it on the special remote side,
made moveAnnex, on Windows, add back the write bit. This apparently
removes the readonly attribute. See Remote.Directory.removeDirGeneric
which already did the same on windows to allow removing files from the
directory special remote.

The reason that cleanObjectLoc also calls allowWrite is to handle
situations where files have already gotten into git-annex repositories on
Windows with the write bit set. Eg, an older git-annex put them there.
Or perhaps the git-annex repository was populated on some other OS.