Use Gitlab::VERSION to version backups

Previous to this commit, backups were tied to the git revision (SHA1) of
the app at the time the backup:create command was invoked. If the SHA1
at the time of restore was different, the script would refuse to restore
the backup.  This commit loosens this tie so that the backup script only
complains if the value of the Gitlab::VERSION constant is different
between the time of backup and the time of restore.

lib/backup/manager.rb

@@ -7,7 +7,7 @@ module Backup
       s = {}
       s[:db_version]         = "#{ActiveRecord::Migrator.current_version}"
       s[:backup_created_at]  = Time.now
-      s[:gitlab_version]     = %x{git rev-parse HEAD}.gsub(/\n/,"")
+      s[:gitlab_version]     = Gitlab::VERSION
       s[:tar_version]        = %x{tar --version | head -1}.gsub(/\n/,"")
 
       Dir.chdir(Gitlab.config.backup.path)
@@ -87,22 +87,16 @@ module Backup
       settings = YAML.load_file("backup_information.yml")
       ENV["VERSION"] = "#{settings[:db_version]}" if settings[:db_version].to_i > 0
 
-      # backups directory is not always sub of Rails root and able to execute the git rev-parse below
-      begin
-        Dir.chdir(Rails.root)
-
       # restoring mismatching backups can lead to unexpected problems
-        if settings[:gitlab_version] != %x{git rev-parse HEAD}.gsub(/\n/, "")
+      if settings[:gitlab_version] != Gitlab::VERSION
         puts "GitLab version mismatch:".red
-          puts "  Your current HEAD differs from the HEAD in the backup!".red
-          puts "  Please switch to the following revision and try again:".red
-          puts "  revision: #{settings[:gitlab_version]}".red
+        puts "  Your current GitLab version (#{Gitlab::VERSION}) differs from the GitLab version in the backup!".red
+        puts "  Please switch to the following version and try again:".red
+        puts "  version: #{settings[:gitlab_version]}".red
+        puts
+        puts "Hint: git checkout v#{settings[:gitlab_version]}"
         exit 1
       end
-      ensure
-        # chdir back to original intended dir
-        Dir.chdir(Gitlab.config.backup.path)
-      end
     end
   end
 end