parser: Rewrite push parser boundary checks

Remove inaccurate xmlParseCheckTransition check.

Remove non-incremental xmlParseGetLasts check.

Add functions that check for several boundary constructs more
accurately, keeping track of progress in ctxt->checkIndex.

Fixes #439.

include/libxml/parser.h

@@ -311,6 +311,8 @@ struct _xmlParserCtxt {
 
     int                input_id;      /* we need to label inputs */
     unsigned long      sizeentcopy;   /* volume of entity copy */
+
+    int           endCheckState;    /* quote state for push parser */
 };
 
 /**