[Rd] multiple defines of diag

[Terry Therneau]

The current coxme code has functions that depend on bdsmatrix and others
that depend on Matrix, both those pacakges define S4 methods for diag.
When loaded, the message appears:
   replacing previous import ‘diag’ when loading ‘Matrix’ 

Questions:
  1. Do I need to worry about this?  If so, what can I do about it?
I suppose I could add an importFrom directive, but it will be a pain
unless there is an "allbut(diag)" option I'm not aware of.  (I assume
that methods and classes can be listed in importFrom, i.e., there are no
importMethodsFrom or importClassesFrom functions).

  2. If I don't need to worry, is there a way to turn the message off?
I as a developer need to see it, but users don't and it may worry them
unnecessarily.  Updating all 17 of my test/*.Rout.save files is a
nuisance as well, but only a nuisance.

I'd like to upload this to CRAN soon as I have users asking for the
updated lmekin function (which uses Matrix).  In the long term all the
bdsmatrix functions will be replaced by Matrix, but that requires major
changes to C code so "long" is the operative word. 

Thanks,
  Terry T.