Merge branch 'devel-2.2' into devel-2.3

* devel-2.2:
  devel/release: Use release-specific Makefile targets
  Makefile: Add new dist target for releases
  Makefile: Stricter checks for release distchecks

Conflicts:
	Makefile.am: Trivial

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