FixedSetPartitions

Functionality for iterating over the partitions of a set into a fixed
number of subsets. partitions(array,m) relates to partitions(array)
like partitions(n,m) relates to partitions(n).
fixed typo in description in manual
Replaced tabs with spaces
Merge pull request #4887 from Jutho/jjjh/fixedsetpartitions

FixedSetPartitions