dot in wiki slug causes error

Hi,

Just ran into this problem...
We would use the version number, which contains dots (for instance 3.4.2) as wiki slug.

When creating a new page, we reference the version number (with dots) as slug and get no error.
But, when saving the page, we get a 502 (or 500?).

We encounter this issue both on the CE version and this EE version.

Looks to me that we should either correct the bug that makes it impossible to save a wiki page if there's a dot in the slug...
Or make sure that the slug does not contain a dot through form validation.

Also discussed in the forum https://forum.gitlab.com/t/creating-wiki-page-results-in-500-were-sorry-but-something-went-wrong/263

I also am curious about the rationale behind adding .markdown to the wiki file names. Is there anything in the wiki machinery that can not function without it. I stumbled on this issue as I added .md, thinking that it was the convention for markdown files. Does the gitlab wiki have to distinguish between gitlab markdown files and more generic versions of markdown files?

My stumbling around was also enabled by the lack of a guide on how to create gitlab wiki pages and what a slug is.

Added wiki label

This issue is a duplicate of #431 (closed). There is a merge request without a test here: !156 (closed). I think I will add a test for that change.

mentioned in merge request !419 (merged)

Status changed to closed by commit 59d5c779

mentioned in commit 1d85e5ff