XPath 2.0 implementation

In the construct processing-instruction('xxx'), I have removed the check that xxx is a valid NCName. The specification does not require this in the case where the name is included in quotes.

Changes for Schema-Aware Processing

Internal changes have been made to prepare the way for Saxon to become a schema-aware processor. The changes are by way of calls to classes and methods that in this (non-schema-aware) version of Saxon have a dummy implementation. These dummy implementations are generally included in the Configuration object, which will be subclassed in the schema-aware product.