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
```

`man time.h` describes second variable type of timespec is `long` not `time_t`.  Is there any reason why use `time_t` type?

```
time_t  tv_sec    Seconds.
long    tv_nsec   Nanoseconds.
```
http://linux.die.net/man/3/clock_gettime