[Rd] substitute inconsistent output

[Jan Gorecki]

Dear R-devel,

Is there anything that we can do to make output of those call more
consistent? So the first one will return `c(1L, 2L)` rather than
`1:2`. Note that it is not related to compact integer sequence
introduced by altrep, it is reproducible on R 3.1.0 as well.

substitute(v+x, list(x=c(1L,2L)))
#v + 1:2
substitute(v+x, list(x=c(0L,2L)))
#v + c(0L, 2L)

Thank you,
Jan Gorecki