parse_opt_ref_sorting: always use with NONEG flag

The "--sort" parameter of for-each-ref, etc, does not handle negation, and instead returns an error to the parse-options code. But neither piece of code prints anything for the user, which may leave them confused: $ git for-each-ref --no-sort $ echo $? 129 As the comment in the callback function notes, this probably should clear the list, which would make it consistent with other list-like options (i.e., anything that uses OPT_STRING_LIST currently). Unfortunately that's a bit tricky due to the way the ref-filter code works. But in the meantime, let's at least make the error a little less confusing: - switch to using PARSE_OPT_NONEG in the option definition, which will cause the options code to produce a useful message - since this was cut-and-pasted to four different spots, let's define a single OPT_REF_SORT() macro that we can use everywhere - the callback can use BUG_ON_OPT_NEG() to make sure the correct flags are used (incidentally, this also satisfies -Wunused-parameters, since we're now looking at "unset") - expand the comment into a NEEDSWORK to make it clear that the direction is right, but the details need to be worked out Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>