chattr: manpage tidyups

chattr: manpage tidyups

Tidy up the chattr(1) manpage to completely document all
available options, and differentiate those which are read-only
early in the manpage as well.

* Remove "I" from settable attribute list
* add "e" to 2nd list of settable attributes & descriptions
* Note that h/E/I/X/Z are readonly
* Correct "H" to "h" for huge file attribute description
* fix long_name for indexed directory in flags_array

Addresses-Red-Hat-Bugzilla: BZ#502971

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