implement CAST and handle ISCHILDNODE joins

[lsmith77]

SELECT u.*
             FROM [nt:unstructured] AS u
              INNER JOIN [nt:unstructured] AS c ON ISCHILDNODE(c, u)
             WHERE ISDESCENDANTNODE(u, [$newsDataPath])
               AND (u.publishable = true)
               AND (u.publishStartDate IS NULL OR u.publishStartDate <= CAST('$now' AS DATE))
               AND (u.publishEndDate IS NULL OR u.publishEndDate > CAST('$now' AS DATE) OR u.publishEndDate = CAST('2008-01-01T00:00:00.000+01:00' AS DATE))
               AND u.[phpcr:class] = 'Liipch\\NewsBundle\\Document\\NewsItem'
               AND NAME(c) = 'phpcr_locale:$locale'
             ORDER BY u.publishStartDate DESC

[lsmith77]

for the ISCHILDNODE join some inspiration can maybe be taken from #178