Reduce the pages-xxx.img file size significantly (from 2.1M to ~100K for simple counter test)
by not dumping private file pages, that have not yet changed from its file prototype.

If you'll have problems with it, just let me know and comment the definition of PAGE_ANON not
to block your work.

This uses the implemented earlier flag from mincore.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>