Closes #772

The percent_complete method returns a value of 100 when a
ZeroDivisionError occurs. That seems like a very strange default for an
error case, and results in a bug when a milestone has no corresponding
issues (new, empty milestones show 100% completion). This commit changes
the rescue value to 0, and subsequently fixes #1656, which reported this
problem.

**What does this do?**
It adds validation to the creation of a wiki page, that way the user gets real
feedback instead of just a 404 page if the name of the wiki page was invalid

**Why is this needed?**
There are a lot of characters that are not allowed in the creation of a wiki
page, there is even a small text that is saying: Please don't use spaces.
Although we have that text there, we don't actually validate on this. This
commit adds validation on the title and gives the user actual feedback.

**What issues does this fix?**
Fixes http://github.com/gitlabhq/gitlabhq/issues/5357
Fixes https://github.com/gitlabhq/gitlabhq/issues/8565
Fixes https://github.com/gitlabhq/gitlabhq/issues/3913
Fixes https://github.com/gitlabhq/gitlabhq/issues/8166Signed-off-by: NJeroen van Baarsen <jeroenvanbaarsen@gmail.com>

**What does this do?**
It makes sure that when you create a wiki page via the web interface, the
extention is .md instead of .markdown

**Why is this needed?**
When you're using Gollum locally, it will create pages with the .md extention.
Also .md is the best known extention for markdown. This fix will make sure that
if you're using gollum or the webinterface, the extention will be the same.

**What issues does this fix?**
Fixes https://github.com/gitlabhq/gitlabhq/issues/5204Signed-off-by: NJeroen van Baarsen <jeroenvanbaarsen@gmail.com>

Closes #1687
Closes https://github.com/gitlabhq/gitlabhq/issues/9325

Closes #1025

Closes #1676

Closes #1535

Closes https://github.com/gitlabhq/gitlabhq/issues/6745

**Why was this needed?**
The changes are pulled in 7.12.0 but where mistakenly put under 7.11.0

[skip-ci]
Signed-off-by: NJeroen van Baarsen <jeroenvanbaarsen@gmail.com>

if something goes wrong, fall back to the plaintext lexer

Tell new users when their password reset token expires and provide a
link to get a new one.

Fixes #5825

Closes #1598

This makes the memory growth-triggered Sidekiq restarts more reliable by
reducing the chance that Sidekiq ends up in a state where it is not
accepting new jobs but also not shutting down: SIGKILL is more likely to
work than SIGTERM.