xml:parse() fails with "Huge input lookup"

[Alexey Stukalov]

When compiled against libxml2 2.9.0 certain scripts that use xml:parse() function fail to process reasonably large files with the following error:
xml:parse(): loader parsing error: internal error: Huge input lookup

This is because at least in 2.9.0 it's required to set XML_PARSE_HUGE option in XmlContext before parsing big files.
The relevant place to do this is e.g. in XmlLoader::applyLoadOptions() method (src/store/naive/loader_dtd.cpp).
When this flag is set the error goes away.