Optionally support old diffs

Some versions of diff do not correctly detect a missing new-line at the end
of the file under certain circumstances.

When defining NO_ACCURATE_DIFF, work around this bug.

Signed-off-by: Johannes E. Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -55,6 +55,9 @@ all:
 #
 # Define NO_ICONV if your libc does not properly support iconv.
 #
+# Define NO_ACCURATE_DIFF if your diff program at least sometimes misses
+# a missing newline at the end of the file.
+#
 # Define COLLISION_CHECK below if you believe that SHA1's
 # 1461501637330902918203684832716283019655932542976 hashes do not give you
 # sufficient guarantee that no collisions between objects will ever happen.
@@ -403,6 +406,9 @@ else
 endif
 endif
 endif
+ifdef NO_ACCURATE_DIFF
+	ALL_CFLAGS += -DNO_ACCURATE_DIFF
+endif
 
 ALL_CFLAGS += -DSHA1_HEADER=$(call shellquote,$(SHA1_HEADER)) $(COMPAT_CFLAGS)
 LIB_OBJS += $(COMPAT_OBJS)

apply.c

@@ -1142,6 +1142,14 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag)
 		size -= len;
 	}
 
+#ifdef NO_ACCURATE_DIFF
+	if (oldsize > 0 && old[oldsize - 1] == '\n' &&
+			newsize > 0 && new[newsize - 1] == '\n') {
+		oldsize--;
+		newsize--;
+	}
+#endif
+
 	offset = find_offset(buf, desc->size, old, oldsize, frag->newpos);
 	if (offset >= 0) {
 		int diff = newsize - oldsize;