resize2fs: handle exactly-16T filesystems in resize2fs

resize2fs: handle exactly-16T filesystems in resize2fs

Before we go whole-hog on 64-bit e2fsprogs, I wonder if this
is worth considering as a last-minute addition to the 1.41
stream.  Currently, mke2fs will shave a block off an exactly-16T
device to fit*, but resize2fs does not do the same, leading
to some asymmetry.  This patch fixes that up, and allows 16T
devices to be handled more gracefully in offline resize.
(in fact resize2fs will not even open a 16T device, today).

*commit 37d17a65ecb4615546b417038190a41bafca7c51

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>