debugging: XMALLOC_POISON

Compile with -DXMALLOC_POISON=1 to catch errors from using uninitialized
memory returned by xmalloc.

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

git-compat-util.h

@@ -91,6 +91,9 @@ static inline void *xmalloc(size_t size)
 		ret = malloc(1);
 	if (!ret)
 		die("Out of memory, malloc failed");
+#ifdef XMALLOC_POISON
+	memset(ret, 0xA5, size);
+#endif
 	return ret;
 }