window(): feature request

Dear R-developpers,

currently the function window shows the following behaviour, if start or
end is out of range:

x <- ts(1:14,start=c(1950,2),frequency=4)
y <- window(x,start=c(1950,1),end=c(1953,4))

Warning messages: 
1: start value not changed in: window.default(x, ...) 
2: end value not changed in: window.default(x, ...) 

Instead of this I would like it to fill with NAs the values before start(x)
and after end(x). Could this be done by introducing an additional option in
window()? Could you please consider this in future releases? Or is there a
better way to do this using existing functions?

P.S.: Below I have added some code that accomplishes this aim in a separate
function (which is probably an example of akward programming...).