[PATCH] inotify: fix event loss on hardlinked files

People have run into a problem when they do this:

watch (file1, all_events);
watch (file2, some_events);

if file2 is a hard link to file1, some events will be missed because by
default we replace the mask.  The patch below adds a flag IN_MASK_ADD which
will cause inotify to add to the existing mask if present.

Signed-off-by: John McCutchan <ttb@tentacle.dhs.org>
Signed-off-by: Robert Love <rml@novell.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>