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.