Integer partitions

This is similar to submission "24185-partitions" in the exchange, but with the set containing identical elements. The partitioning is a also a way of writing the input n as a sum of positive integers.

An optional argument s can be supplied to output a subset of partitions with number of parts less than or equal to s.

The number of ways of partitioning is according to the sequence
http://oeis.org/A000041

Example 1: intpartition(4) gives {[1 1 1 1],[1 1 2],[1 3],[2 2],4}
Example 2: intpartition(10,2) gives {[3,7],[4,6],[5,5],10}