JJTree generated parser for parsing and creating XPath ASTs.

Implementation notes (Apr-03-sc): The actual grammar.xml from the XPath spec is transformed using a series of XSLT stylesheets into various inputs for the javacc/jjtree process. JJTree then generates the parser, which gets checked in; this includes many of the .java files in this package - so don't go editing the .java files themselves without checking if they're generated!

Check carefully that you're using the correct grammar file, since until the XPath 2.0 specs are final, we have several experimental versions of the grammar checked in (Apr-03-sc).