get_all_vars fails with matrices (PR#13624)

Hi,

According to the help file for model.frame/get_all_vars, the following should 
produce the same output from both functions, but it doesn't...

dat <- list(X=matrix(1:15,5,3),z=26:30)
model.frame(~z+X,dat)

z X.1 X.2 X.3
1 26   1   6  11
2 27   2   7  12
3 28   3   8  13
4 29   4   9  14
5 30   5  10  15

get_all_vars(~z+X,dat)

[1] z    X    <NA> <NA>
<0 rows> (or 0-length row.names)

-- the equivalent works ok if there are no matrices involved. 

I'm using  R version 2.9.0 alpha (2009-03-24 r48212) (Suse linux 10 and 11, 64 
bit intel). I found the problem while trying to fix a problem in an mgcv 
plotting routine.

best,
Simon

> Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK
> +44 1225 386603  www.maths.bath.ac.uk/~sw283