Upgrade libxml2 to 2.7.3 to patch some vulnerabilities.
diff --git a/error.c b/error.c
index 722ffbb..5f03d94 100644
--- a/error.c
+++ b/error.c
@@ -31,7 +31,7 @@
 								\
     size = 150;							\
 								\
-    while (1) {							\
+    while (size < 64000) {					\
 	va_start(ap, msg);					\
   	chars = vsnprintf(str, size, msg, ap);			\
 	va_end(ap);						\