Fix SYSINFO_memory on Mac OS X

f_system on OS X was always saying 0MB because SYSINFO_memory was not filled in. Fill it in.

NOTE: There are some fixmes a few lines above, I left in.

Before:

![before](https://f.cloud.github.com/assets/11351/2059581/b6d74d38-8bbc-11e3-9c76-df7e4e60916b.png)

After:

![after](https://f.cloud.github.com/assets/11351/2059582/bb9a7d4a-8bbc-11e3-886c-d954e2fbc4bd.png)