[Rd] as.matrix.dist patch (performance)

[Tim Taylor]

Please find attached a small patch to improve the performance of 
as.matrix.dist().  It's a tiny bit more involved than the current code 
but does bring a reasonable speed improvement for larger <dist> objects 
(remaining comparable for smaller ones).

Example:

set.seed(1)
dat <- matrix(rnorm(20000), ncol = 2);
system.time(as.matrix(dist(dat)))

As of r84931:

    user  system elapsed
   3.370   1.154   4.535

With this patch:

    user  system elapsed
   1.925   0.754   2.685

Submitting here in the first instance but happy to move to Bugzilla if 
more appropriate.

Cheers

Tim

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