update gitlab shell to 1.9.8 for gitlab 7.2.2

As committed in https://github.com/gitlabhq/gitlabhq/commit/873acfd9aa54e801d5786c32b05c4f8ad21af72a GitLab 7.2.2 requires GitLab Shell 1.9.8. Fixes https://github.com/gitlabhq/gitlabhq/issues/7806.
improve 7.3 upgrade process & redius setup

Fixes
https://github.com/gitlabhq/gitlabhq/commit/2b35c887904b6a7a05a7c88fdf1ccd66ba943e20#commitcomment-7829537,
https://github.com/gitlabhq/gitlabhq/commit/5704e6fee9d2dea67c4a91b43d06a9958484d29b#commitcomment-7829367,
&
https://github.com/gitlabhq/gitlabhq/commit/5704e6fee9d2dea67c4a91b43d06a9958484d29b#commitcomment-7829381
Save last scrollposition and scroll back when leaving ZEN mode
Merge pull request #7809 from bbodenmiller/patch-25

update gitlab shell to 1.9.8 for gitlab 7.2.2
Merge pull request #7812 from bbodenmiller/7.3-upgrade

improve 7.3 upgrade process & redis setup
Merge pull request #7815 from Razer6/zen/fix_scroll_position

Save last scrollposition and scroll back when leaving ZEN mode
Replace old spinach step definitions with step.
Improve the wording explaining protected branches.
Add wisdom about reverting a revert merge.
Revert "Diff headers made sticky."

This reverts commit 6eb85b1a30eb2e87fc6a55d17bb38fdf535a516b.
Merge branch 'revert_sticky_headers' into 'master'

Revert sticky headers

See merge request !1104
Version 7.3.0.
Update manual installation guide for the correct shell version.
Support sockets in 'rake gitlab:shell:install'
Merge branch 'shell_install_socket'

Conflicts:
	doc/install/installation.md
Prefix Spinach features with Spinach::Features::.
Time for 7.4.0-pre.
Order of tasks in monthly release doc.
Add steps for building and deploying gitlab.com packages to monthly release document.
Update monthly release doc that we are not using travis anymore.