[R] appeal --- add sd to summary for univariates

[ivo welch]

just a short beg for the next R 2.3 version:

I know it is easy to add the sd into summary() in the source bowels of
R---but everytime R is updated, my change disappears.  :-(.  I do not
believe that R has an easy extension mechanism for univariate
summaries, short of a function rewrite here.  Could this please be
added into R 2.3?

Aside, a logical ordering might also be:
   mean sd min q1 med q3 max
rather than have mean buried in between order statistics.

regards,

/iaw