Merge branch 'nd/magic-pathspec' into maint

"git diff -- ':(icase)makefile'" was unnecessarily rejected at the
command line parser.

* nd/magic-pathspec:
  diff: restrict pathspec limitations to diff b/f case only

t/t6131-pathspec-icase.sh

@@ -100,4 +100,10 @@ test_expect_success 'match_pathspec_depth matches :(icase)bar with empty prefix'
 	test_cmp expect actual
 '
 
+test_expect_success '"git diff" can take magic :(icase) pathspec' '
+	echo FOO/BAR >expect &&
+	git diff --name-only HEAD^ HEAD -- ":(icase)foo/bar" >actual &&
+	test_cmp expect actual
+'
+
 test_done