use string_list initializer consistently

use string_list initializer consistently

There are two types of string_lists: those that own the
string memory, and those that don't. You can tell the
difference by the strdup_strings flag, and one should use
either STRING_LIST_INIT_DUP, or STRING_LIST_INIT_NODUP as an
initializer.

Historically, the normal all-zeros initialization has
corresponded to the NODUP case. Many sites use no
initializer at all, and that works as a shorthand for that
case. But for a reader of the code, it can be hard to
remember which is which. Let's be more explicit and actually
have each site declare which type it means to use.

This is a fairly mechanical conversion; I assumed each site
was correct as-is, and just switched them all to NODUP.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>