Merge branch 'devel-2.3'

* devel-2.3:
  cfgupgrade: Remove unused “program” variable
  cfgupgrade: Check master name, clarify question
  Makefile: Merge build-time reST copying
  Move doc/upgrade.rst to UPGRADE, copy at build-time
  Import upgrade notes into documentation

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>