[R] Test for pre-existing Win menu or item

[Jeff Gentry]

> Before using winMenuAdd(), is it possible to test whether the menu already 
> exists? One could use try(winMenuAddItem()) with appropriate arguments, but 
> is there anything more elegant?

winMenuNames() and winMenuItems() should give you the sort of information
you're looking for, tho they're in R-devel and not R-1.8.x.

-J