Set version to 2.6.0.

git-svn-id: http://svn.redmine.org/redmine@13436 e93f8b46-1217-0410-a6f0-8f06a7374b81
Added 2.6-stable branch.

git-svn-id: http://svn.redmine.org/redmine@13437 e93f8b46-1217-0410-a6f0-8f06a7374b81
Set version to stable.

git-svn-id: http://svn.redmine.org/redmine@13438 e93f8b46-1217-0410-a6f0-8f06a7374b81
Japanese translation updated by Go MAEDA (#18069)

git-svn-id: http://svn.redmine.org/redmine@13439 e93f8b46-1217-0410-a6f0-8f06a7374b81
Merged r13439 from trunk to 2.6-stable (#18069)

Japanese translation updated by Go MAEDA.

git-svn-id: http://svn.redmine.org/redmine@13440 e93f8b46-1217-0410-a6f0-8f06a7374b81