Added Parser::recursivePreprocess(); like preprocess() but doesn't call startParse...

Added Parser::recursivePreprocess(); like preprocess() but doesn't call startParse() so that it can be used inside a parse operation using the same context without having to mess with other functions

Simple use case (PHP 5.3+) that will work show the expand text passed to a <preprocess> tag:
$wgHooks['ParserFirstCallInit'][] = function( $parser ) {
	$parser->setHook( 'preprocess', function( $text, $attr, $parser, $frame ) {
		return $parser->recursivePreprocess( $text, $frame );
	} );
	return true;
};