support encfs4win

This is a companion to #1074

This issue affects the Windows version of encfs (encfsmp)

Brief description:

I suspect that this might be related to a per-user drive letter vs. a systemwide drive letter.

I have some important information stored on an encfs-encrypted drive letter. The Windows tool to mount such drives is encfsmp (http://encfsmp.sourceforge.net/) Drive letters mounted by encfsmp are not visible in /mnt/. Due to the nature of data I store encrypted, this is a show stopper for me. Note: the Linux version of encfs also does not work; I will enter a separate problem report for that.

• Expected results

• In Windows, run encfsmp to mount an encrypted drive as drive letter K: My other drive letters are C: and E:

• In Explorer, verify that the K: drive exists and is accessible.

• ls /mnt should show
  c e k

• Actual results (with terminal output if applicable)

  ls /mnt
  c e

• Your Windows build number
  14393

• Steps / All commands required to reproduce the error from a brand new installation

• Install encfsmp from http://encfsmp.sourceforge.net/

• Create an encrypted file system (Note: in my situation, the file system was originally created on a Linux system, and copied to the Windows system) and add some files.

• Add the encrypted file system to encfsmp as a mount named "MyVolumeName"

• Mount an encrypted file system. The command line I use is:
  "C:\Program Files\EncFSMP\EncFSMP.exe" mount -m MyVolumeName

• Start bash

• run ls /mnt

• Strace of the failing command
  N/A

• Required packages and commands to install
  On Windows: encfsmp.exe from http://encfsmp.sourceforge.net/

See our contributing instructions for assistance.

Start by reproducing the reported behavior on Windows build 14393: mount an encrypted filesystem with EncFSMP as K: and compare Explorer with ls /mnt. Investigate how mounted Windows drive letters are discovered, and consider the issue complete when the encfsmp-mounted drive appears under /mnt and the existing reproduction steps pass.