[ADMB Users] ADMB and MinGW-w64 users should update

[dave fournier]

I did a bit of experimenting with writing large buffers to disk and it 
appears that
replacing the low level  writes with fwrites and open with fopen etc .  
permits one
to write large buffers to disk in the code.

A more interesting solution might be to optionally  add another thread 
which can write
portions of the buffer to disk as they become full.