GH-90: Windows Client Compatibility

This patch fixes two issues to make knife-solo work properly on windows clients:
 * on a windows client use `>NUL` instead of `>/dev/null`
 * when using a cygwin-compiled rsync.exe on a windows client 
  * the permissions [are messed up](http://stackoverflow.com/questions/5798807/rsync-permission-denied-created-directories-have-no-permissions) and need to be set explicitly via `--chmod=ugo=rwX`
  * the source path must be adjusted a la `/cygdrive/...` 

_Note:_ the assumption is that you have a cygwin-compiled ssh.exe and rsync.exe on the PATH, otherwise it won't work due to the `system "rsync..."` calls