Eng 6265 add format currency func

Add a SQL function, FORMAT_CURRENCY. Its function is return a string in xx,xxx,xxx.xx format given a number. 
This implementation seems much more complicated than required.
Decimal should only be slightly more code than INTEGER etc.
In fact, the simplest treatment is probably:
   extract the integer part and append to the stream just as above.
   extract the fractional part in some convenient format, truncate it to two digits, convert the two digits to string with leading 0 as needed, append "." and two-digit string to stream.
    I was surprised to find that VALUE_TYPE_DECIMAL is not handled at all in some of the type conversion functions in NValue.hpp and I believe that this is strictly an oversight -- it should only complain about values out of range when it is passed specific values that are actually out of range, not just "potentially" out of range based only on the range of the DECIMAL type.
Yet, there ARE examples you can use/modify for how to extract the whole and fractional parts of our scaled TTInt representation for decimals -- see NValue.hpp lines 1013 and 1122.