[BUILD] Changes necessary for Release 13.12.6

This patch updates:
 * Version numbers
 * Feature description
 * Update-site
 * Changelog
 * Credits

Change-Id: Ife69291d3e06dae43b5bf9f500aa3cb83192a4db
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1286
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
Reviewed-by: Andrej Szaffranietz <a.szaffranietz@gmail.com>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
[HACK] ensure reply to newer version requests

This hack ensures that the next release will at last receive a version
too old response. Neverless it is not possible vice versa.

Change-Id: I85b9ad9299ed092f0b8a66224466eb909a0d8c08
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1278
Tested-by: Jenkins CI
Reviewed-by: Andrej Szaffranietz <a.szaffranietz@gmail.com>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>