Error handlers not set correctly

[tewha]

Per the libxml2 documentation for xmlSetStructuredErrorFunc:

Function to reset the handler and the error context for out of context structured error messages. This simply means that @handler will be called for subsequent error messages while not parsing nor validating. And @ctx will be passed as first argument to @handler For multi-threaded applications, this must be set separately for each thread.

Unfortunately, KissXML only attempts to set these functions as part of +initialize. Instead, they need to be installed each time a call is made into the library that could fail.

This is probably a fairly large issue, and potentially unfixable at the library level; having a public class method to install the error handlers would probably be sufficient. This way, code intentionally using KissXML off the main thread could specifically initialize the error handlers.

[tewha]

I take back this being a difficult problem to solve in the library: There are only a couple places where KissXML checks the error. It's easy enough to call a new [DDXMLNode installErrorHandlersInThread] there.

[tewha]

Obsoleted by pull request #24.