diff-patch: Avoid emitting double-slashes in textual patch.

Signed-off-by: NJunio C Hamano <junkio@cox.net>

diff.c

@@ -211,6 +211,8 @@ static void emit_rewrite_diff(const char *name_a,
 	diff_populate_filespec(two, 0);
 	lc_a = count_lines(one->data, one->size);
 	lc_b = count_lines(two->data, two->size);
+	name_a += (*name_a == '/');
+	name_b += (*name_b == '/');
 	printf("--- a/%s\n+++ b/%s\n@@ -", name_a, name_b);
 	print_line_count(lc_a);
 	printf(" +");
@@ -1020,8 +1022,8 @@ static void builtin_diff(const char *name_a,
 	const char *set = diff_get_color(o->color_diff, DIFF_METAINFO);
 	const char *reset = diff_get_color(o->color_diff, DIFF_RESET);
 
-	a_one = quote_two("a/", name_a);
-	b_two = quote_two("b/", name_b);
+	a_one = quote_two("a/", name_a + (*name_a == '/'));
+	b_two = quote_two("b/", name_b + (*name_b == '/'));
 	lbl[0] = DIFF_FILE_VALID(one) ? a_one : "/dev/null";
 	lbl[1] = DIFF_FILE_VALID(two) ? b_two : "/dev/null";
 	printf("%sdiff --git %s %s%s\n", set, a_one, b_two, reset);