disables the option explicitely.
Changed the option location in code so that --help will show it in
lexical option order.

This is for bug #26215: mysql command line client should not strip
comments from SQL statements


client/mysql.cc:
  Changed the help text for --comments to make it clear which option
  disables the option explicitely.
  Changed the option location in code so that --help will show it in
  lexical option order.