o completion after $ works on names().  This is not OK for non-list named 
   objects.  On the other hand, we want to be able to $ completion on other 
   objects that have a $method.  Not sure what the best approach would be.

 o make filename completion work better.  Do it in R?

 o what are the .__* things in S4 namespaces?  Need to filter these out.

> getNamespaceExports("stats4")
 [1] "AIC"                 "BIC"                 ".__C__mle"
 [4] "coef"                "confint"             ".__C__profile.mle"
 [7] ".__C__summary.mle"   "logLik"              ".__M__AIC:stats"
 ...
> stats4::.__C__mle

Slots:

Name:       call      coef  fullcoef      vcov       min   details minuslogl
Class:  language   numeric   numeric    matrix   numeric      list  function

Name:     method
Class: character
> .__C__mle
Error: object ".__C__mle" not found