Merge tag 'v2.6.0'

Merge tag 'v2.6.0'

Git 2.6

* tag 'v2.6.0': (479 commits)
  Git 2.6
  Git 2.6-rc3
  send-email: fix uninitialized var warning for $smtp_auth
  l10n: de.po: better language for one string
  l10n: de.po: translate 2 messages
  l10n: Update and review Vietnamese translation (2440t)
  l10n: fr.po v2.6.0 round 2 (2440t)
  l10n: zh_CN: for git v2.6.0 l10n round 2
  l10n: ca.po: update translation
  l10n: git.pot: v2.6.0 round 2 (3 improvements)
  l10n: de.po: translate 123 new messages
  l10n: fr.po v2.6.0 round 1 (2441t)
  Update RelNotes to 2.6
  Git 2.5.3
  mailmap: update my entry with new email address
  Update RelNotes to 2.6 to describe leftover bits since -rc2
  Git 2.6-rc2
  poll: honor the timeout on Win32
  doc: show usage of branch description
  gitk: Accelerators for the main menu
  ...