Improve XPath error messages
Commit 954b8984 removed some extra XPath error messages which were only reported to the global error handler. In a few cases, these error messages contained helpful information which is lost now. For example
- Unregistered function: which function?
- Undefined variable: which variable?
- Undefined namespace prefix: which prefix?
We should add an extra string argument to xmlXPathErr
which is added to error messages and structured errors.