Borrowed from a3f0e28 that was supposed to land in the now-closed tj#1921.

(cherry picked from commit 87db4ba)

Analogous to 3c94dfd in tj#1933 for version option.

Storing the Option instance of the help option instead of just its
flags (_helpShortFlag, _helpLongFlag) is meaningful for cases when other
properties of the instance need to be accessed (not currently the case,
but could be in the future).

Eliminates outputHelpIfRequested() and incorporates help option parsing
into .parseOptions() instead for consistency with other options.

Additionally, improvements to the .parseOptions() code have been made,
first and foremost to the comments.

Eliminates the need for the check in other places.

(cherry picked from commit a12f5be)

…ption-refactor

…ption-refactor

Achieved by giving up the earlier introduced 'option:' events for help
and a better .parseOptions() design.

The default command now concedes the help option to the parent in
exactly the same cases in which all other options would be conceded.

Add a displayHelp property to the returned object indicating whether a
help flag had been found before encountering a subcommand, or before
giving up option processing in favor of subcommands due to passThroughOptions being enabled.

Before encountering a subcommand, the help option is now consumed in
exactly the same cases any other option would be consumed.

So that the help option is correctly consumed.

This reverts commit eae6c5f.

Only the help flags are consumed after an unknown option is encountered
and before a subcommand or a command-argument is encountered when using
passThroughOptions.

As a result, when a help flag is encountered in this stage of option
processing,
- the help is consumed by the parent command rather than by the
  subcommand if a subcommand is encountered later or a default
  command is provided;
- the help is displayed instead of an unknown option error
  even when not using allowUnknownOption.

Only stop processing from parent when a sub-subcommand or a
command-argument is encountered. Before that, known options found after
an unknown one are consumed by the parent, including the help option.

Includes a partial fix for tj#1936 (docs need an update, too)

(cherry picked from commit a8b656d)

Reverts to original conditionals structure so that implicitly invoked
default commands behave as if the command name came before the first
arg that is not a known option, and not as if it came before the first
arg that is not an option (known or unknown) like previously.

Fixes pass through and handling of options after the unknown for
implicitly invoked default commands.

Eliminates redundant calls and checks.

- Store onlyKnownOptionsSoFar value instead of computing
- Removed passThroughOptions comment considered unclear (see tj#1942)

(cherry picked from commit d7e2399)

This reverts commit e8bea4a.

…ption-refactor