Change menu item to "Logout [user's name or username]"

Adds the operator's full name (if present) or their username to the Logout menu item.
Use get_username() instead of directly accessing the username field
Oops, use get_username()
Test for Django version > 1.5
Use >= 1.5, not > 1.4
OR… just use cms.utils.compat.DJANGO_1_4… doh!
Forgot one
Merge pull request #3045 from mkoistinen/add_user_name_to_logout_menu

Change menu item to "Logout [user's name or username]"