bugfix in buffer object. Didn't increase the refcount when slicing

examples/rosetta_code/99_bottles_of_beer.noja

@@ -18,7 +18,6 @@
 #
 # ==================================
 
-stringFromInteger = import("../int_to_str.noja").stringFromInteger;
 cat = string.cat;
 
 fun verse(n: int)

examples/rosetta_code/arithmetic_and_geometric_mean.noja

@@ -1,10 +1,3 @@
-Numeric = int | float;
-
-fun abs(n) {
-	if n < 0:
-		return -n;
-	return n;
-}
 
 # Calculate the arithmetic-geometric mean of x,y.
 fun agm(x: Numeric, y: Numeric,