soft freeze for 0.16

[David Bremner]

Hi Gang;

I'll be off the grid for about 12 days, starting on Friday. I thought
that made pretty good sense as a freeze time. On the other hand, I
realize people may have a few last minute items (hopefully small) for
0.16, so I will consider such suggestions when I get back.

I have merged master to the release branch, so other people with push
access need not feel inconvenienced by this freeze; do let me know by
email of any thing that should be cherry-picked/merged to the release
branch later.

d