Add Boolean Data Type to Pig

Introduce boolean as first class Pig data type. You can use "boolean" anywhere Pig expecting a data type. For example: a = load 'input' as (a0:boolean, a1:tuple(a10:boolean, a11:int), a2); b = foreach a generate a0, a1, (boolean)a2; c = group b by a2; -- group by a boolean field When UTF8StorageConvert converts bytes into boolean, it expects "true" (ignore case) to be TRUE and "false" (ignore case) to be FALSE, otherwise, we get null. For example: a = load 'input' as (a0:boolean); input file: true -- we get TRUE True -- we get TRUE FALSE -- we get FALSE 1 -- we get null We also change the interface LoadCaster/StoreCaster to include boolean type.