perf: add basic sort performance test

Add a sort command to test-string-list that reads lines from stdin,
stores them in a string_list and then sorts it.  Use it in a simple
perf test script to measure the performance of string_list_sort().

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

t/perf/p0071-sort.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+test_description='Basic sort performance tests'
+. ./perf-lib.sh
+
+test_perf_default_repo
+
+test_expect_success 'setup' '
+	git ls-files --stage "*.[ch]" "*.sh" |
+	cut -f2 -d" " |
+	git cat-file --batch >unsorted
+'
+
+test_perf 'sort(1)' '
+	sort <unsorted >expect
+'
+
+test_perf 'string_list_sort()' '
+	test-string-list sort <unsorted >actual
+'
+
+test_expect_success 'string_list_sort() sorts like sort(1)' '
+	test_cmp_bin expect actual
+'
+
+test_done