pull: use git-rev-parse --parseopt for option parsing

pull: use git-rev-parse --parseopt for option parsing

To enable unambiguous parsing of abbreviated options, bundled short
options, separate form options and to provide consistent usage help, use
git-rev-parse --parseopt for option parsing. With this, simplify the
option parsing code.

Signed-off-by: Paul Tan <redacted>
Signed-off-by: Junio C Hamano <redacted>