allocate only as much as is needed

ensureCapacity would allocate up to 50% too much memory

primitiveCollections/src/main/java/org/lucares/collections/IntList.java

@@ -1065,7 +1065,7 @@ public final class IntList implements Serializable, Cloneable {
 		// TODO use a more efficient algorithm. Especially the removeIf is too
 		// expensive, because of all the method calls
 		final IntList result;
-		result = new IntList();
+		result = new IntList(a.size() + b.size());
 		result.addAll(a);
 		result.addAll(b);
 		result.sort();