* Made it possible to configure the parser class being used, via $wgParserConf.
* Moved defines from the top of Parser.php to either class constants or Defines.php
* Added Parser_DiffTest, a differential parser class for regression testing
* Added Parser_OldPP, a parser class which operates like the parser before this commit. I made one breaking change: a bugfix to avoid losing whitespace when adding MWTEMPLATESECTION markers.
* Made internal tidy work with PHP 5
* Added the ability to supply a hook for template fetching via ParserOptions. This is handy for testing.
* Updated parserTests.txt to account for the various breaking changes I made. Removed a few parser tests that no longer test for anything useful.
