Don't use tr1/memory on recent Mac OS X versions

The newer SDKs for Mac OS X don't have the <tr1/memory>
headers, you can use just <memory>.
This adds a check of the system Mac version in setup.py and
if it is 10.9 or later add's the flag -D NO_TR1_MEMORY to the
compiler arguments. Then that's used in an #if in POIIndex.h
to use <memory> instead of <tr1/memory>.

Seems to work on my Mac running 10.10, but I wasn't running into this issue
anyway because conda's Python targets the Mac 10.5 SDK.