Make Kore compilation compatible with OSX

Kore was not compiling on OSX throwing the following errors:

```
src/domain.c:75: error: ‘SSL_MODE_RELEASE_BUFFERS’ undeclared (first use in this function)
src/domain.c:75: error: (Each undeclared identifier is reported only once
src/domain.c:75: error: for each function it appears in.)
...
Undefined symbols for architecture x86_64:
  "_setresgid", referenced from:
      _kore_worker_entry in worker.o
  "_setresuid", referenced from:
      _kore_worker_entry in worker.o
  "_setproctitle", referenced from:
      _kore_platform_proctitle in bsd.o
```

This fix resolves those errors ensuring Kore compiles fine and works as desired on OSX.

Tested with:
Macbook Air Mid-2012 with OSX Mountain Lion 10.8.2