A release build is just a snapshot from the SVN repository at a specific moment in time.
r29005 is the very latest (as of this writing) SVN revision, and 3.7 was tagged at r28402
r29005 isn't the "unofficial" anything, it's simply one of the *many* revisions made to the repository on a daily basis.
Every so often, new additions are to the repository are "frozen" for a release, and for ~2 weeks or so developers attempt to work on outstanding issues in preparation for tagging another release.
[St.]