[Rd] Segfault with options() (PR#7078)

[deepayan at stat.wisc.edu]

This is completely undocumented use of options, but it does cause a 
segfault with r-patched and r-devel on Linux:

options(list('digits', 'scipen'))

Strangely enough, 

options(list('digits'))

and 

options(list(digits = 10, scipen = 2))

work as might be expected.

Deepayan