Issue-4769 - Unable to update case of label

Labels are saved in the database with the case they were originally created with.
Before this change if a user created a label with the same text but different case
the label would use the original case and no new label would be created in the
database. With this change, labels are now case-sensitive.

Steps to test:

1. Before this change, create a new issue with a new label "FIxMe"
2. Edit the issue and change the label to "FixMe"
3. Note that the label reverted to "FIxMe"
4. Apply this change
5. Edit the issue again and change the label to "FixMe"
Note that the new case was preserved. If you also look in the database in the "tags" table you will see that both labels are present - "FIxMe" and "FixMe".
Add instructions to install Git from source

This is needed for Ubuntu 12.04, which only provides Git 1.7.9.
Edit config/gitlab.yml when compiling git
Divide Git installation instructions in two
Include full dependencies for Git compilation
Clarify that Git 1.8.x is OK
Add a combined update doc from 5.1 to 6.0
Fix for issue #5431
Merge branch 'install_git_from_source' of /home/git/repositories/gitlab/gitlabhq
Merge pull request #5436 from Seed-Of-Hate/master

Fix for issue #5431
Restore sidekiq rake tasks
Report application status through init exit code
Merge branch 'fix_sidekiq_rake' of /home/git/repositories/gitlab/gitlabhq
Update installation.md

Updated instructions to include proper stable. Otherwise they fail due to Rack extensions required below.
Reset button/link on the reset password page. Fixes #5418
Merge pull request #5448 from flewid/patch-1

Update installation.md
Merge pull request #5453 from perryfaro/password-page

Reset buttons/links on the reset password page
Better font size for projects list on dashboard
rounded avatars
Reduce font-size for event-title