PL3118 and PL3131 fix: provide new option "--barrier" to showattr and

PL3118 and PL3131 fix: provide new option "--barrier" to showattr and
setattr to set the barrier bit. Also use the correct ext2 attribute
bits if possible; immulink changed from bit 15 to bit 27 in 2.6.x. Also
provide bit clearing options such as those provided in 0.30.196
(i.e. "--!immutable" or "--~immutable", remember to backslash the ! and
~ characters on the command line).

This program sucks. The 0.30.196 version isn't much better. We should
just hack e2fsprogs chattr.