Fix: accept 255 character labels

Example:

 # /home/jsakkine/devel/smack/utils/chsmack \
   -a$(printf '12345%.0s' {1..51}) foo
 foo: Invalid argument
 # /home/jsakkine/devel/smack/utils/chsmack \
   -a$(printf '12345%.0s' {1..51} | head -c -1) foo
 #

This patch fixes this issue.
utils/chsmack: fix hazardous option parsing

The variable option_index was only set to a proper value if the
given option is a long option. There was also exit() missing on
error condition if SMACK label was invalid.

This patch removes option_index, parameter name from corresponding
error message and adds exit() call when the error condition
realizes.

[jarkko.sakkinen@linux.intel.com: rewrote patch description]
Add parameter name back to the chsmack error message

This patch add parameter name back to the error message. Instead
of relaying on hazardous longindex parameter of getopt_long(), a
look-up table is constructed to map short option to the corresponding
struct option entry.

Additionally, the basename of the application is added to the error
message. Also usage message is converted to use basename instead of
the full path name.