Bug#150831: maybe document this?

[Ross Boylan <ross@biostat.ucsf.edu>]

I just got bit by this too.  I agree the behavior is unexpected.

Perhaps, pending changing the behavior, it could be documented--maybe in
the discussion of the --purge option: "Note this will not work if the
package has already been removed."
-- 
Ross Boylan                                      wk:  (415) 502-4031
530 Parnassus Avenue (Library) rm 115-4          ross@biostat.ucsf.edu
Dept of Epidemiology and Biostatistics           fax: (415) 476-9856
University of California, San Francisco
San Francisco, CA 94143-0840                     hm:  (415) 550-1062