Mac OSX compatibility changes

I had to change CMAKE_OSX_DEPLOYMENT_TARGET to 10.7. Apparently that is a compatibility mode that makes the compiler use older libraries.  This is documented here:

http://stackoverflow.com/questions/19637164/c-linking-error-after-upgrading-to-mac-os-x-10-9-xcode-5-0-1

I also added `-std=c++11 -lc++abi` according to this:

http://stackoverflow.com/questions/7016730/compiling-with-clang-using-libc-undefined-references

Tests now pass on my machine.