Preselect the current issue tracker with selected="selected"

The previous behavior was, that the first element of the select was
preselected, thus upon saving the project, the previous selected could
be overwritten.
Add security warnings to update docs
Bump gitlab-shell in 5.4 and 6.2
Add 5.1-to-5.4 update path
Clarify upgrade steps
Add security update info to 6.0-to-6.2.md
Support -ms-linear-gradient style for IE10+
Fix name of RHEL

The company is called Red Hat, and its flagship product is Red Hat Enterprise Linux (commonly abbreviated as RHEL). There is no such thing as RedHat (and never was).
Always show namespace for project title

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'ui/namespace_title' of /home/git/repositories/dzaporozhets/gitlabhq
Merge branch 'master' of github.com:gitlabhq/gitlabhq
Merge branch 'security_update_master' of /home/git/repositories/gitlab/gitlabhq
Merge pull request #5528 from mcepl/patch-1

Fix name of RHEL
Merge pull request #5521 from mynetx/ie10-css-gradients

Support -ms-linear-gradient style for IE10+
Merge pull request #5507 from jojosch/project-issue-tracker-selection

Preselect the current issue tracker with selected="selected"
Merge branch 'master' of dev.gitlab.org:gitlab/gitlabhq
Include gitlab-shell in patch update doc
Merge branch 'gitlab_shell_in_patch_doc' of /home/git/repositories/gitlab/gitlabhq
Number 3 was missing.
Merge branch 'consistent-numbering' of /home/git/repositories/gitlab/gitlabhq