rev-list: remove last static vars used in "show_commit"

rev-list: remove last static vars used in "show_commit"

This patch removes the last static variables that were used in
the "show_commit" function.

To do that, we create a new "rev_list_info" struct that we will pass
in the "void *data" argument to "show_commit".

This means that we have to change the first argument to
"show_bisect_vars" too.

While at it, we also remove a "struct commit_list *list" variable
in "cmd_rev_list" that is not really needed.

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