Merge branch 'devel-2.3'

* devel-2.3:
  Correct version check for release candidates
  config.py: need explicit %-formatting in errors.OpPrereqError.
  Fix version check
  Add script to check version format

Conflicts:
	Makefile.am

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>