I just ran rebuild -r tickets/DM-6168 afw on OS X El Capitan in python 3 and it installed correctly. There were a few minor version differences from Tim's:

pyyaml: 3.11.lsst1+3 ok (4.1 sec)

python_psutil: 4.1.0+3 ok (3.8 sec)

0.3.7.lsst1+2 ok (4.6 sec)

pyfits: 3.4.0+7 ......ok (27.9 sec)

log: tickets.DM-6168-g1c87a4e726 ok (8.3 sec)

daf_persistence: tickets.DM-6168-g40cf864c45 ok (31.1 sec)

but nothing major.

I'll note that this was a fresh install (meaning I cloned lsstsw into a new folder and ran a rebuild on a new stack), other than a symbolic link to afwdata.

I can't reproduce this problem.
I have tried building with rebuild -r tickets/DM-6168 afw on my Mac with Python 2 and 3.
Additionally I have tried new Jenkins Python 2 and 3 builds (of afw) and both Fred Moolekamp and Nate Lust have built it without problems.
Unsure how to proceed.

Is it possible that neither you nor Nate Lust nor Fred Moolekamp have the lsst-db credentials? Are the daf_persistence tests skipping for you? That would explain everything. Pim Schellart [X] I'll send you the special file – you really need it for your testing (Jenkins does not have it so the DB tests are skipped).

Yes, that was it. The tests were skipped both on my machine and on Jenkins.
I added the credentials and added the missing wrapper for DbStorage.

With the caveat that I haven't checked every line and I assume the code that exists on master is now back on the branch, this all looks fine and my build of afw did complete on Python 3.