bisect: use new "struct argv_array" to prepare argv for "setup_revisions"

bisect: use new "struct argv_array" to prepare argv for "setup_revisions"

Because we will use other instances of this struct.

The "rev_argv_push" function is changed into 2 functions
"argv_array_push" and "argv_array_push_sha1" that take a "struct
argv_array *" as first argument. And these functions are used to
simplify "bisect_rev_setup".

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>