prepos_mutex.h is dependant on pthread and is not Windows supported

```
pthread is not by default in Windows.

Either:
- add installation instructions in README
- disable prepos_mutex.h in mili.h until support is added
- ifdef implementatino of prepos_mutex and implement it in Windows

```

Original issue reported on code.google.com by `esteban....@gmail.com` on 7 Jan 2012 at 10:47
