Merge branch 'stable-2.6'

* stable-2.6:
  Make Diffy in Diffy theme smaller
  Remove unnecessary @SuppressWarnings annotations in ChangeControl
  Update documentation to clarify how to set Global Capabilities
  Distinguish between error and timeout in intraline diff error message
  Replace Hashtable with ConcurrentMap
  Fix login redirect loop when auth.type = HTTP
  Include site header, footer and CSS on OpenID login form
  TrivialRebase: Fix custom categories