Took it from https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/3232

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Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_17981421

All this does is convert the version sections into headers. The list
items shouldn't really be indented by two spaces, but it makes no
difference to the rendering and this way we retain authorship history
for the actual changes.

Related to https://gitlab.com/gitlab-org/release-tools/merge_requests/29

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Update migrating_from_svn.md document on migration from SVN to GitLab as suggested by @axil in MR 6549.

Documentation updated to cover Git/SVN mirror approach to migration from SVN to GitLab.

Split into user and administrator docs:

- administration/issue_closing_pattern.md
- user/project/issues/automatic_issue_closing.md

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- Fixed and added specs.
- Added different namespace options depending on user privilages
- Updated docs.

Revert "Revert all changes introduced by https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6043"

This reverts commit 6d43c95b.

# Conflicts:
#	lib/gitlab/github_import/importer.rb

Now the alias should be used as:

    git mr upstream 5

To check out a MR number 5 from the upstream remote, into a `mr-upstream-5`
local branch.

Also clarify that the `5` in the merge request is the number shown in GitLab.