e2fsprogs: revise and extend chattr(1) and chattr usage()

e2fsprogs: revise and extend chattr(1) and chattr usage()

The chattr(1) manpage and chattr usage() output were missing some flags.

Add those, and make some other minor cosmetic fixes.

(I've left out the 'B' (EXT2_COMPRBLK_FL) flag, because
it's not actually used anywhere, and I can't figure out
how it differs from 'c' (EXT2_COMPR_FL))

Also, because the matrix of filesystems & flags is quite large,
refer to filesystem-specific manpages for detailed discussion
of flags supported by those filesystems, rather than trying to
cover it all in this manpage.  I'll send those manpage
updates to the appropriate lists a bit later.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>