Inventive hack to get flex raising exceptions on parse error

Inventive hack to get flex raising exceptions on parse error

The core of this (over 2500 lines) patch reads as follows:
-    fprintf(stderr, "%s\n", flexml_err_msg);
+    surf_parse_error(flexml_err_msg);

But the code we want to change is generated by Flex, so ... I have to
augment the perl script that rewrite some parts of the Flex result for
that purpose. Because yes, we do have such a perl script.

At the end, we need to regenerate the flex parser with the latest
version of Flex to apply this patch, resulting in that jumbo patch.