Update libxml to 2.7.7.

third_party/libxml/schematron.c

Index: third_party/libxml/schematron.c
diff --git a/third_party/libxml/schematron.c b/third_party/libxml/schematron.c
index 81f47044bbf4d2094570c8979fefdbdf968371be..07709e2440880ad693c1f3696728a865cb20f6d9 100644
--- a/third_party/libxml/schematron.c
+++ b/third_party/libxml/schematron.c
@@ -1425,7 +1425,7 @@ xmlSchematronReportSuccess(xmlSchematronValidCtxtPtr ctxt,
                         (pattern == NULL)?NULL:((const char *) pattern->name),
                         (const char *) path,
                         (const char *) report, 0, 0,
-                        msg);
+                        "%s", msg);
     } else {
 	xmlSchematronReportOutput(ctxt, cur, &msg[0]);
     }
@@ -1691,7 +1691,7 @@ xmlSchematronValidateDoc(xmlSchematronValidCtxtPtr ctxt, xmlDocPtr instance)
 		if (xmlPatternMatch(rule->pattern, cur) == 1) {
 		    test = rule->tests;
 		    while (test != NULL) {
-			xmlSchematronRunTest(ctxt, test, instance, cur, rule->pattern);
+			xmlSchematronRunTest(ctxt, test, instance, cur, (xmlSchematronPatternPtr)rule->pattern);
 			test = test->next;
 		    }
 		}