blame: use DEFINE_LIST_SORT

blame: use DEFINE_LIST_SORT

Build a typed sort function for blame entries using DEFINE_LIST_SORT
instead of calling llist_mergesort().  This gets rid of the next pointer
accessor functions and their calling overhead at the cost of a slightly
increased object text size.

Before:
__TEXT	__DATA	__OBJC	others	dec	hex
24621	56	0	147515	172192	2a0a0	blame.o

With this patch:
__TEXT	__DATA	__OBJC	others	dec	hex
25229	56	0	151702	176987	2b35b	blame.o

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>