Coreutils enhancement: ls: add colorization of mountpoints

[Parke]

Hello, coreutils@gnu.org,

I am contemplating extending ls so that mountpoints can be colorized
(via LS_COLORS).

If I implement this change, I would be happy to contribute it to
Coreutils, if the maintainers want this change.

My use case:  I want to be able to quickly distinguish Btrfs
subvolumes (and ZFS datasets) from plain directories.

I'm hoping that a mountpoint can be detected by comparing the st_dev
fields returned by calling stat() on a directory and on that
directory's parent.

There are some related choices:  Should non-directory mounts also be
colorable?  Should mount colors be subdivided as directories are,
namely: based on the sticky-bit and the other-writable-bit.

Comments welcome.

Cheers,

Parke