completion: add --option completion for most builtin commands

completion: add --option completion for most builtin commands

Many builtin commands use parseopt which can expose the option list
via --git-completion-helper but do not have explicit support in
git-completion.bash. This patch detects those commands and uses
__gitcomp_builtin for option completion.

This does not pollute the command name completion though. "git <tab>"
will show you the same set as before. This only kicks in when you type
the correct command name.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>