[SPARK-4358][SQL] Let BigDecimal do checking type compatibility and use more specified numeric types 

Remove hardcoding max and min values for types. Let BigDecimal do checking type compatibility.
Okay, sorry, I realize I initially said this was a good idea.  Thinking about it further though I'm not sure if this is actually something we want to do.  The memory benefits of picking the smallest possible number representation don't really seem to outweigh the added complexity of having to deal with bytes everywhere all of a sudden.

Are there any other SQL systems that do this?

To be clear I am in favor of using BigDecimal's `isValidX` instead of our hand coded checking for int/long/bigdecimal