Drop custom version of search_env_filtered

It's now available in the utils cookbook, and having the two versions
create a conflict (with one overloading the other).

(cherry picked from commit 0a05de3e61e9b9ad655a50e5fb13d2c4b9b862ca)
Removed the single assignment block from constraints

(cherry picked from commit 0d3754a9294eee3ba4474d8bb3d785f43b7d5d19)
Merge pull request #333 from vuntz/release/stoney/master

Sync with roxy