The shortcut of these options do not make much sense when used with
switch. And their descriptions are also tied to checkout. Move -b/-B
to cmd_checkout() and new -c/-C with the same functionality in
cmd_switch_branch()
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>