Lots of comments/questions on this function - at different levels.

* The function name doesn't match the convention used elsewhere.  We typically use camel case.

* We also tend to provide a boolean argument to enable the setting to be set.  e.g., void setPageCacheFlush()

* I also wonder whether it is worth making it more general purpose.  It depends if there is likely to be any more file specific options?  E.g., maybe we would like an option to set read ahead?

In this case we should have something along the lines of

```
enum IFIOoptions
{
 IFIOnopagecache = 0x0001,
 IFIOreadahead = 0x0002,
}

void setOptions(IFIOoption options);
```

* Finally I wonder if the flag should be passed to IFile::open, with the implementations passing it on to the IO classes instead.  Having it in the interface theoretically allows it to be called after the file has been read/written from.  It feels more like an option that should be set at object construction.

@richardkchapman, @jakesmith what do you think?