add mac wheels for 10.9 / 64b only

[robbuckley]

followup to #46, which was partly reverted after merging.

resolves #42 for the daily branch.

additional changes compared to #46:

• config.sh is back compatible with older versions of the multibuild submodule
• 10.9 builds are the default, it makes .travis.yml a little cleaner to read

[robbuckley]

i will test the wheels locally tomorrow

[jreback]

lgtm. ping when ready for merge.

[robbuckley]

should be good to go. I've tested the 3 osx wheels from the build on my fork, all pass.

BTW the multibuild commit for this is on their devel branch. The advice on https://github.com/matthew-brett/multibuild/ README is:

We try to keep the master branch stable and do testing and development in the devel branch. From time to time we merge devel into master.

In practice, you can check out the newest commit from devel that works for you, then stay at it until you need newer features.

[jreback]

thanks @robbuckley