stable as subset of develop

[Brett Porter <porter@devrts.com>]

In a small group, develop is the branch where all fixes/additions/... from topic
branches are merged rather dynamically. Thorough testing of commits may lag behind,
but when we think one is a pretty good commit we want to identify it as (at least
relatively) the latest stable. We could tag it, but we would like these stable commits to
be a branch in the sense that each commit points back to a previous commit.

Merging from a development branch commit to stable isn't quite what we want. It seems
more like:

   checkout the new good development commit
   change HEAD to the head of the stable branch
   git add --all
   git commit
   (maybe tag the new commit with the hash of the chosen development commit)

Will that work (one thing beyond my current understanding is if there are index complications)?
Other ideas?

This could help with applying successively more intense testing over time and chase down
where problems arose.