add--interactive.perl: factor out repeated --recount option

add--interactive.perl: factor out repeated --recount option

Depending on the direction and the target of patch application, we would
need to pass --cached and --reverse to underlying "git apply".  Also we
only pass --check when we are not applying but just checking.

But we always pass --recount since 8cbd431 (git-add--interactive: replace
hunk recounting with apply --recount, 2008-07-02).  Instead of repeating
the same --recount over and over again, move it to a single place that
actually runs the command, namely, "run_git_apply" subroutine.

Signed-off-by: Junio C Hamano <gitster@pobox.com>