Port to Mavericks.

This patch depends on https://github.com/jubatus/jubatus-mpio/pull/13/files.
Build commands are following:

```
./bootstrap
CXXFLAGS="-std=c++11 -DMP_FUNCTIONAL_STANDARD -DMP_MEMORY_STANDARD -DMP_UNORDERED_MAP_STANDARD" ./configure
make
make install
```

There is no reason to use ```time_t```. I will fix it.