I'm not sure why it was disallowing '/' in paths; the only reason I could think of was security, so I've disallowed '..' instead. I'm pretty sure there are angles here I haven't thought of, so use at your own risk :)
A quick thought: on Linux, '/' is the root directory, similarly to "C:\" on Windows. Perhaps this was the reason it's verboten. An opening slash should either be disallowed, or treated as a relative link.
