Add Bigdecimal functions in Over function

-4 new functions: SUM, AVG, MAX and MIN for BigDecimal and 4 test for each function. -An another outputschema. This output takes the inner alias and type of inputschema and returns the same alias with "_over" and the type. This is because in a foreach like the next: x = FOREACH SUM { ini = FOREACH test GENERATE id, id_2; GENERATE FLATTEN(MYSTITCH(ini, MYOVER(test.impt_prima, 'sum(bigdecimal)'), MYOVER(test.impt_1, 'sum(bigdecimal)'), MYOVER(test.impt_2, 'sum(bigdecimal)'))); with the normal OVER function the foreach fails because all MYOVERS return the same alias.