We have a problem with file locks (bug #2512) -- the /proc/locks
file shows the ID of lock creator, not the owner. Thus, if the
creator died, but holder is still alive, criu fails to dump the
lock held by latter task.

The proposal is to find who _might_ hold the lock by checking
for dev:inode pairs on lock vs file descriptors being dumped.
If the creator of the lock is still alive, then he will take
the priority.

One thing to note about flocks -- these belong to file entries,
not to tasks. Thus, when we meet one, we should check whether
the flock is really held by task's FD by trying to set yet
another one. In case of success -- lock really belongs to fd
we dump, in case it doesn't trylock should fail.

At the very end -- walk the list of locks and dump them all at
once, which is possible by merge of per-task file-locks images
into one global one.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>