Fix "apply --reverse" with regard to whitespace

"git apply" used to take check the whitespace in the wrong
direction.

Noticed by Daniel Barkalow.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-apply.c

@@ -1003,12 +1003,16 @@ static int parse_fragment(char *line, unsigned long size, struct patch *patch, s
 			trailing++;
 			break;
 		case '-':
+			if (apply_in_reverse &&
+					new_whitespace != nowarn_whitespace)
+				check_whitespace(line, len);
 			deleted++;
 			oldlines--;
 			trailing = 0;
 			break;
 		case '+':
-			if (new_whitespace != nowarn_whitespace)
+			if (!apply_in_reverse &&
+					new_whitespace != nowarn_whitespace)
 				check_whitespace(line, len);
 			added++;
 			newlines--;

t/t4116-apply-reverse.sh

@@ -82,4 +82,10 @@ test_expect_success 'apply in reverse without postimage' '
 	)
 '
 
+test_expect_success 'reversing a whitespace introduction' '
+	sed "s/a/a /" < file1 > file1.new &&
+	mv file1.new file1 &&
+	git diff | git apply --reverse --whitespace=error
+'
+
 test_done