diff.h: move pickaxe fields together again

Move the pickaxe and pickaxe_opts fields next to each other again. In
a past life they'd been on adjacent lines, but when they got moved
from a global variable to the diff_options struct in 6b5ee137e5 (Diff
clean-up., 2005-09-21) they got split apart.

That split made sense at the time, the "char*" and "int" (flags)
options were being grouped, but we've long since abandoned that
pattern in the diff_options struct, and now it makes more sense to
group these together again.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.h

@@ -265,6 +265,7 @@ struct diff_options {
 	 * postimage of the diff_queue.
 	 */
 	const char *pickaxe;
+	unsigned pickaxe_opts;
 
 	/* -I<regex> */
 	regex_t **ignore_regex;
@@ -304,8 +305,6 @@ struct diff_options {
 	/* The output format used when `diff_flush()` is run. */
 	int output_format;
 
-	unsigned pickaxe_opts;
-
 	/* Affects the way detection logic for complete rewrites, renames and
 	 * copies.
 	 */