error: Limit number of parser errors

Reporting errors is expensive and some abusive test cases can generate
an error for each invalid input byte. This causes the parser to spend
most of the time with error handling. Limit the number of errors and
warnings to 100.

include/libxml/parser.h

@@ -310,6 +310,8 @@ struct _xmlParserCtxt {
     unsigned long      sizeentcopy;   /* volume of entity copy */
 
     int           endCheckState;    /* quote state for push parser */
+    unsigned short     nbErrors;    /* number of errors */
+    unsigned short   nbWarnings;    /* number of warnings */
 };
 
 /**