Only trigger search if search string is present

This is a follow up for !296 to prevent the search function from being executed while the query is nil.

Problem was this:
When the search is called, the search controller gets 2 requests.
```
{"action"=>"show", "controller"=>"search"}
```
and
```
{"utf8"=>"✓",
 "search"=>"proj",
 "project_id"=>"",
 "group_id"=>"",
 "snippets"=>"",
 "scope"=>"",
 "button"=>"",
 "action"=>"show",
 "controller"=>"search"}
```

Obviously it doesn't make sense to execute the search for the first request, since that one doesn't have a scope or a search string.

Please review this carefully since this modifies the search and may break things i can't think of.

@dzaporozhets While this fixes the root cause for the failing test, I think we should keep your fix in as a failsafe. What do you think of this?

See merge request !302

Backup repo with tar instead of git bundle

Fixes gitlab/gitlab-ee#246

See merge request !1723

Fewer Git constants, more Git helpers.

See merge request !1727

Fix link to 'URL auto-linking' section in markdown help

Update rugments, fixes #8976

Fixed spelling mistake in install docs

Fixed spelling mistake of this.

[ci skip]

See merge request !404

Remove success signin message by devise

I find it really annoying every time I login into GitLab it shows me
that I successfully signed in. But this makes no sense to me. I already
see dashboard and dont see login screen. Its obvious I signed in
successfully. Instead it just show annyoing message every time taking
part of space on my screen.

See merge request !401

Show test settings as disabled when service cannot be tested.

See merge request !1725

You get redirected after signuout to gitlab.com and see this message on login page which makes no sense.

I find it really annoying every time I login into GitLab it shows me
that I successfully signed in. But this makes no sense to me. I already
see dashboard and dont see login screen. Its obvious I signed in
successfully. Instead it just show annyoing message every time taking
part of space on my screen.

Improve UI

* Improve group rename warning
* Refactor select css. Make selects same width

See merge request !400

Improve diffs UI

* replace big button with simple toggle for diff comments
* replace diff stats button with link

See merge request !399

Handle nil restricted visibility settings

Return `true` from `non_restricted_level?` when the `restricted_visibility_levels` setting is nil.  This addresses #2154.

cc @sytse

See merge request !1724

Added binstub for guard

Return `true` from `non_restricted_level?` when the
`restricted_visibility_levels` setting is nil.

This reverts commit 7602cef5.