Use long filenames by default on FAT filesystems

Use long filenames by default on FAT filesystems

These days, 8.3 filenames are often a problem, filesystems containing
firmware with long names must not truncate them -- it's also a sane default
as portable file system between OSes, anyway.

Altough undocumented in mount_msdos(8), the default for FAT32 already is to
use long filenames:  ever since its import from NetBSD in 1998.

Previously, mount_msdos would ignore long filenames and default to short
filenames unless a flag was used or long ones were found on the filesystem
prior to mounting it.

Just always mount with support for long filenames (unless `-s' is used).

As various install media use FAT filesystems, adjust the remaining ones to
also pass explicit mount option reflecting the previous default.

OK deraadt