[KBFS] Support for symbolic link to location underneath a Keybase TLF?

Hello,

This is my environment:

Environment: Windows 10 Pro
Keybase: 1.0.15-20160503112215+243eebf

Creating a symbolic link outside Keybase that links to a location somewhere under a Keybase TLF seems to work OK in OSX but when I try an equivalent operation in Windows 10, it doesn't work. I have a Keybase path like this:

```
K:\private\salshyn\travel\countries\test.txt
```

After that I make a symbolic link like this:

```
mklink /D "C:\Users\salshyn\Downloads\Test" "K:\private\salshyn\travel"
```

The symbolic link is created but I can't access it. When trying to `cd` into `C:\Users\salshyn\Downloads\Test\countries` I get an error saying:

```
The system cannot find the path specified.
```

And through file explorer, double-clicking on the `countries` folder I get a dialog box that reads:

`Location is not available.
C:\Users\salshyn\Downloads\Test\countries is unavailable. If the location is on this PC, make sure the device or drive is connected or the disc is inserted, and then try again. If the location is on a network, maker sure you're connected to the network or Internet, and then try again. If the location still can't be found, it might have been moved or deleted.`

Can someone let me know a) whether this kind of symbolic linking is supported and b) to the degree it is supported, should what works on OSX also work on Windows?

Thanks in advance!

Start by reproducing the Windows 10 case with the provided mklink command and the K:\private\salshyn\travel path, then compare it with the reported macOS behavior. Trace the Windows KBFS path handling involved in symbolic-link traversal; done means establishing whether this is supported and documenting the expected behavior or a reproducible fix target.

Written by the indexing model from the issue text.