Added Windows tar support to Vagrant export

 - Windows tar seems to only be happy with fully qualified paths
   in a *nix style, so instead of C:\Folder\Two or C:/Folder/Two
   it wants /C/Folder/Two
 - Tested against Tar 1.2.2 on Windows
Merge pull request #567 from Iristyle/patch-1

Added Windows tar support to Vagrant export