swap / iter_swap consistency, and brief introduction

[chris]

Relating toswap / iter_swap discussions, I see that in some places 
swap(*a,*b); is being used in places where iter_swap should perhaps be 
used (in rotate and __partition. __partition is particularily bad as the 
ForwardIterator case uses swap() and the BidirectionalIterator case uses 
iter_swap()).

In these cases we know that the types given are the same, so the 
"iter_swap can take different types" problem doesn't arise. However it 
would I assume be sensible to syncronise on one or the other.. (if 
iter_swap was changed to use swap then iter_swap would be the obvious 
choice.. if not it might require more thought).

Chris