Changes to Saxon extensions and extensibility mechanisms

An additional flag is provided for saxon:deep-equal(): the I flag tests whether the is-ID and is-IDREF properties of two nodes match.

To allow XSLT extension instructions to be called from generated bytecode, the interface has been changed: evaluation must now be done using the standard call method, which is aligned with the interface for integrated extension functions. For examples, see the source code of the SQL extension classes.