FxGqlC: Added support for DateTime datatype

SELECT convert(string, convert(datetime, '2012-07-13'), 'yyyyMMdd HH:mm:ss') 
-- Formats datetime using a format string, as defined by the .net Framework
--   "Standard Date and Time Format Strings" (http://msdn.microsoft.com/en-us/library/az4se3k1), and 
--   "Custom Date and Time Format Strings" (http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx)
SELECT datepart(day, '2012-07-13') -- returns 13
-- valid datepart values are: (with examples for '2012-07-12 23:59:50.1234567')
--    year,        yy, yyyy :   2012
--    quarter,     qq, q    :         3  (1 ... 4)
--    month,       mm, m    :         7  (1 ... 12)
--    dayofyear,   dy, y    :       194  (1 ... 366) 
--    day,         dd, d    :        12  (1 ... 31)
--    weekday,     dw, w    :         5  (1 = Sunday ... 7 = Saturday)
--    hour,        hh, h    :        23  (0 ... 23)
--    minute,      mi, n    :        59  (0 ... 59)
--    second,      ss, s    :        50  (0 ... 59)
--    millisecond, ms       :       123  (0 ... 999)
--    microsecond, mcs      :    123456  (0 ... 999999)
--    nanosecond,  ns       : 123456700  (0 ... 999999900)
SELECT dateadd(day, 10, '2012-07-03')
-- returns 2012-07-13
SELECT datediff(day, '2012-07-03', '2012-07-13') 
-- returns 10
SELECT datediff(day, '2012-07-12 23:59', '2012-07-13 00:01') 
-- returns 1, the number of day-boundaries crossed (as in T-SQL)
SELECT datediff(day, '2012-07-13 23:59', '2012-07-13 00:01') 
-- returns 0
SELECT datediff(day, '2012-07-14 23:59', '2012-07-13 00:00')  
-- returns -1
SELECT getdate(), getutcdate() 
-- returns current DateTime in local and UTC/GMT time