Show referenced MRs & Issues only when the current viewer can access them

This addresses both issues identified in #6066.

## The private MR by user `remy2` with a note referencing to a public issue

![Screen_Shot_2016-01-12_at_16.45.02](/uploads/c245ec2c1fdea1f9ba05183c24e142d9/Screen_Shot_2016-01-12_at_16.45.02.png)

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## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** before the fix

![Screen_Shot_2016-01-12_at_18.14.50](/uploads/8db5580e803f5bddd6cb935233c579a0/Screen_Shot_2016-01-12_at_18.14.50.png)

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## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** with the fix

![Screen_Shot_2016-01-13_at_12.02.32](/uploads/cb199f7b78191fba486a11412412e307/Screen_Shot_2016-01-13_at_12.02.32.png)

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## The public issue viewed by user `remy2` with the fix (no change)

![Screen_Shot_2016-01-13_at_11.54.06](/uploads/ddece590d69f597a95559beddcd36660/Screen_Shot_2016-01-13_at_11.54.06.png)


See merge request !2405

Update button style on milestone pages

See merge request !2414

Update documentation to Go 1.5.3

Security fix: https://groups.google.com/forum/#!topic/golang-dev/MEATuOi_ei4

See merge request !2418

Fix the undefinded variable error in Project's safe_import_url method

Fixes #7982

See merge request !2419

Fix has been introduced in !2224.

Move doc_styleguide in the development directory

Reference #3841 

And also add many new styleguides:

- Naming
- Images
- Links
- Headings
- Formatting
- Notes
- API

See merge request !2386

Added hint that you can search users by name, username, or email.

Fixes gitlab-org/gitlab-ee#19

/cc @JobV 

See merge request !2411

- Fix some syntax/grammar typos
- Link to GFM documentation on newlines
- Be less strict on the alphabetical order styleguide
- You can override the "numbers in headings" rule if you discuss it first
- Do not mention CE in notes if the feature is in both CE and EE

See merge request !2406

Fix #9963 reference_filter "Encoding::CompatibilityError" bug with some complex URL;

https://github.com/gitlabhq/gitlabhq/pull/9964

@DouweM

See merge request !2383

Extend projects API with CI data

Reference #4264 

See merge request !2303

enable milestone filter to stick



See merge request !2241

Sampling data at a fixed interval means we can potentially miss data
from events occurring between sampling intervals. For example, say we
sample data every 15 seconds but Unicorn workers get killed after 10
seconds. In this particular case it's possible to miss interesting data
as the sampler will never get to actually submitting data.

To work around this (at least for the most part) the sampling interval
is randomized as following:

1. Take the user specified sampling interval (15 seconds by default)
2. Divide it by 2 (referred to as "half" below)
3. Generate a range (using a step of 0.1) from -"half" to "half"
4. Every time the sampler goes to sleep we'll grab the user provided
   interval and add a randomly chosen "adjustment" to it while making
   sure we don't pick the same value twice in a row.

For a specified timeout of 15 this means the actual intervals can be
anywhere between 7.5 and 22.5, but never can the same interval be used
twice in a row.

The rationale behind this change is that on dev.gitlab.org I'm sometimes
seeing certain Gitlab::Git/Rugged objects being retained, but only for a
few minutes every 24 hours. Knowing the code of Gitlab and how much
memory it uses/leaks I suspect we're missing data due to workers getting
terminated before the sampler can write its data to InfluxDB.

merge request close message moved and merge request now refered by `!`.

Fixes #4161 

![Screen_Shot_2016-01-12_at_8.38.57_AM](/uploads/9390ce0ebd1d14bfc83130ff4913a823/Screen_Shot_2016-01-12_at_8.38.57_AM.png)

See merge request !2387

Disable colorization if STDOUT is not a tty

Closes #6118 

See merge request !2403

Block the reported user before destroying the record

This is intended to prevent the user from creating new objects while the
transaction that removes them is being run, resulting in objects with
nil authors which can then not be edited.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/7117

See merge request !2402

Make sure time_ago_with_tooltip is using a Time object

Somehow this test existed on EE but not in CE, so it started failing
after a bad CE-to-EE merge.

See merge request !2398

Comment and close button does not submit comment



See merge request !2399

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Include the user_id in user_*_team system hooks.

Mention channel/key bug in irkerd docs

It patches core classes (such as String) to add colorization methods
like `red` which we can't disable the same way we can with the
Colorization gem.

This is intended to prevent the user from creating new objects while the
transaction that removes them is being run, resulting in objects with
nil authors which can then not be edited.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/7117

Prepare Installation and Update docs for 8.4 RC1

[ci skip]

See merge request !2401

[ci skip]

Per this issue: https://gitlab.com/esr/irker/issues/2

A documentation update was added to irkerd (https://gitlab.com/esr/irker/commit/190808c37d4ab5f0f16fe35352ff36863c2732d5) but the bug is still there. Making a note of it here could save someone a lot of hassle. 

This could probably be worded better if someone else wants to take a stab at it.

Revert "Remove the `:coffee` and `:coffeescript` Haml filters"

This reverts commit ae7de2f8.

Several files in EE still use the `:coffeescript` filter and
I don't have time to fix them before the CE-to-EE merge.

See https://gitlab.com/gitlab-org/gitlab-ee/builds/553647

I will reintroduce this change in a future MR.

See merge request !2400

This reverts commit ae7de2f8.