Replace `-slash-` by a neutral separator (`_`)

[thom4parisot]

I find the -slash- thingy quite disturbing to read. A single character would do the trick.

[julien-nc]

The "-slash-" has much less chances to get a name collision than an underscore.

What if a directory contains a file named a/b and another one named a_b?

Also, allowing slashes in names is not very standard (never seen it somewhere else) and I would recommend not to do it.