hygiene, declare this copy of nifty.h ours

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, provide fops.h to mmap() (and munmap()) whole files based on the descriptor

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, hide open()/stat()/mmap() guts behind mmap_fn() in fops.h

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, actually include sys/stat.h for fstat() in fops.h

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, follow-up, also include fcntl.h and unistd.h for open() and close() in fops.h

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/aux'

* core/aux:
  minor, follow-up, also include fcntl.h and unistd.h for open() and close() in fops.h
  minor, actually include sys/stat.h for fstat() in fops.h
  minor, hide open()/stat()/mmap() guts behind mmap_fn() in fops.h
  minor, provide fops.h to mmap() (and munmap()) whole files based on the descriptor
  hygiene, declare this copy of nifty.h ours