[R] draw.key; getting grobWidth to respect fontfamily="mono"

[Benjamin Tyner]

Update: seems one way to skin this cat is to add

   gp = gpar(fontfamily="mono")

to the viewport() call itself. If anyone has any suggestions for a 
robust way to extract this piece information from the key grob itself 
(it's nested several levels deep), I'm all ears.

Thanks
Ben