misc: handle very large files with filefrag

misc: handle very large files with filefrag

Avoid overflowing the column-width calc printing files over 4B blocks.

Document the [KMG] suffixes for the "-b <blocksize>" option.

The blocksize is limited to at most 1GiB blocksize to avoid shifting
all extents down to zero GB in size.  Even the use of 1GB blocksize
is unlikely, but non-ext4 filesystems may use multi-GB extents.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Lustre-bug-id: https://jira.whamcloud.com/browse/LU-13197
Signed-off-by: Theodore Ts'o <tytso@mit.edu>