* options can now be spelled "foo-bar" or "foo_bar" (handled in
    'parse_config_files()', just after we parse a file)
  * added a "[global]" section so there's a place to set global
    options like verbose/quiet and dry-run
  * respect the "negative alias" dictionary so (eg.) "quiet=1" is
    the same as "verbose=0" (this had to be done twice: once in
    'parse_config_file()' for global options, and once in
    '_set_command_options()' for per-command options)
  * the other half of handling boolean options correctly: allow
    commands to list their boolean options in a 'boolean_options'
    class attribute, and use it to translate strings (like "yes", "1",
    "no", "0", etc) to true or false