Merge branch 'devel-2.1'

* devel-2.1:
  Bump up version to release 2.1.6
  Update NEWS file for 2.1.6

Conflicts:
	NEWS
	  - merge
	configure.ac
	  - keep 2.2 version

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>