String Permutation Class

Permutation to permutate a string (short one) to return subsets... with variable parameters. "ABC" returns a,b,c,aa,ab,ac,ba,bb,...abc,aca,acb ... (Initially implemented with a recursive solution there was the bothersome stack overflow and also other minor problems... later when implemented with a tripple for loop it still fails the volume test though try not to have too many characters or it will exceed phps 30sec execution. Any body has better solutions to this can email me :p)