[Rd] R-lang edit: deparse(1:2) is no longer a good example of the R parser's non-invertibility

[Josh O'Brien]

Hello,

Apparently thanks to improvements to the R parser, this example from
section 6.1 of the R Language Definition no longer holds.

> deparse(quote(c(1, 2)))
[1] "c(1, 2)"
> deparse(1:2)
[1] "c(1, 2)"

Even running R-2.14.2, I get instead

> deparse(1:2)
[1] "1:2"