Add local file system option to disable UNC on Windows.

This will add an option to disable UNC conversion on Windows to deal with buggy file system implementations like EncFS.

Fixes #261

docs/content/local.md

@@ -36,3 +36,37 @@ will emit a debug message in this case (use `-v` to see), eg
 ```
 Local file system at .: Replacing invalid UTF-8 characters in "gro\xdf"
 ```
+
+### Long paths on Windows ###
+
+Rclone handles long paths automatically, by converting all paths to long
+[UNC paths](https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath)
+which allows paths up to 32,767 characters.
+
+This is why you will see that your paths, for instance `c:\files` is
+converted to the UNC path `\\?\c:\files` in the output,
+and `\\server\share` is converted to `\\?\UNC\server\share`.
+
+However, in rare cases this may cause problems with buggy file
+system drivers like [EncFS](https://github.com/ncw/rclone/issues/261).
+To disable UNC conversion globally, add this to your `.rclone.conf` file:
+
+```
+[local]
+nounc = true
+```
+
+If you want to selectively disable UNC, you can add it to a separate entry like this:
+
+```
+[nounc]
+type = local
+nounc = true
+```
+And use rclone like this:
+
+`rclone copy c:\src nounc:z:\dst`
+
+This will use UNC paths on `c:\src` but not on `z:\dst`.
+Of course this will cause problems if the absolute path length of a
+file exceeds 258 characters on z, so only use this option if you have to.